DE-MYSTIFYING ELECTRICAL SYSTEMS ON MERIDEN TRIUMPHS

By Pete Kinlyside – TriumphRat.net “OzBloke”

This paper attempts to explain the intricacies of Meriden Triumph electrical systems. The idea for the paper was born from my own challenges with these systems, and from the many electrical questions being raised by other owners on the TriumphRat.net Classics web forum. I’ve tried to explain how things work in two formats; the simple non-technical format, and the deeper technical format. It’s not meant to replace workshop manuals, but to supplement them. Hopefully it will help those who want to maintain and fault-find these sometimes frustrating but always amazing older bikes.

First, some terms you might see or hear when working on your bike, and which I use in this paper

Term MeaningEarth The common return path for electrical current, usually the frame

of the bike, plus the engine. Aka: frame, chassis or ground.Voltage The measure of electricity force or “pressure”, measured in

VoltsCurrent The measure of electricity flow, stated in AmpsResistance The measure of resistance of a certain component to current

flow, measured in Ohms ( Ω ), or Kilohms (1000 Ohms or K Ω ), or Megohms ( 1 million ohms or M Ω )

Short aka. Short circuit. A path for current that bypasses vital components – usually associated with a fault, resulting in high current flow, burnt wires, blown fuse, bad smells, and sometimes fire.

Open Circuit A broken path, which does not allow current to flow, Usually associated with broken wires, poor connectors, blown fuse, or faulty components.

High-tension The high voltage connection from the secondary of the ignition coil to the spark plug – the spark plug lead.

RFI Radio Frequency Interference. Electronic noise radiating from electrical components due to magnetic fields generated by current flowing through a conductor.

1. Ignition Systems

This section explains the inner working of Meriden Triumph ignition systems, from the basics such as the theory behind the system, to the more advanced areas like Boyer ignition systems.

Ignitions systems are built from a combination of components. For most older bikes, these are:

The battery

The fuse The ignition switch The engine kill switch The points (aka breaker points, contact points) The condenser (aka capacitor) The coil(s) The spark plug(s) The wires between the various components, in particular the plug leads.

For the sake of simplicity, take it for granted that I’m explaining things using a single cylinder at this point. Not much difference with a twin or triple cylinder engine, where most components are duplicated, except when you get into the electronic systems such as Boyer.

Simple Science

One terminal of the battery is connected to earth. Most modern bikes are negative ground, while the older Meriden Triumphs are positive earth. Positive earth (or positive ground) means that the positive terminal of the battery is directly wired to the frame/engine of the bike to provide the return path for the electrical current.

The other terminal of the battery is wired to the fuse, then from the other side of the fuse to the ignition switch, and from there to the kill switch, and from the kill switch to one side of the coil (in the Meriden case, the negative terminal of the coil). With the ignition switch off, no current flows to the coil, and no spark can be produced. With the ignition switch and the kill switch both in the “on” position, 12 volts is applied to one side of the coil.

The coil is basically a 1:100 transformer. It has a primary side, being the two screw/blade terminals on top for positive and negative 12 volts connections. The other half is called the secondary or high tension winding. One end of the secondary winding connects to the negative terminal, while the other end connects to the insulated cup connector on the top, into which the plug lead is connected.

The set of points, operated by the camshaft, acts as an on/off switch for the positive side of the coil to earth. When the points are closed, current flows from the battery, through the fuse, through ignition and kill switches, through the coil, through the points contacts, to the engine, and finally back to the positive side of the battery via wires and/or frame. At this stage, the condenser, which is wired across the points, is not charged, as the points short it out. Diagram 1 illustrates the components and the current path.

This current flow quickly creates an electromagnet inside the coil. While the points are closed, this magnetic field remains stable. At a point in the rotation of the camshaft, a lobe on the points cam causes the points to open. Current is no longer flowing through the coil, and the magnetic field collapses. This collapsing magnetic field causes a voltage to be generated in the secondary coil. The condenser comes into play now, as it’s no longer being shorted by the points. It has a dual function – to help pump up the primary voltage, and to drastically reduce sparking across the points. The primary voltage goes up to around 300-400 volts, and the secondary voltage leaps to 20-30 thousand volts.

This secondary voltage is sufficient to jump the gap between the spark plug centre electrode and the side (ground) electrode, and current flows from the coil secondary, through the spark plug, through the engine to the frame, through the condenser, to the negative terminal of the coil. When the voltage being developed is no longer sufficient to jump the gap, the spark stops.

Extra-Technical Explanation

As the points open, the magnetic field around the primary winding of the coil begins to collapse. This induces a voltage across the secondary and primary windings. The condenser initially acts as a short until it starts to charge. This stops arcing across the points contacts. As the voltage builds across both the secondary and primary, no current is yet flowing through the secondary, as the current path is not yet establish across the spark plug gap. Around 400 volts can be developed across the primary winding as the condenser becomes fully charged. Depending on the spark plug gap, and the state of the fuel vapour /air mix between the plug electrodes, at a certain voltage, the vapour will ionise, and allow current to pass. This commences the spark. As the current flows through the secondary winding, the condenser discharges through the primary, thereby inducing more voltage across the secondary, which elongates the spark time. This “loop” effect continues in a decreasing cycle until the

Battery

FuseIgn Sw Kill Sw

Coil

Condenser

Points

SparkPlug

DIAGRAM 1

Current Flow

capacitor no longer holds sufficient charge to induce enough voltage in the secondary to maintain the ionisation of the plug gap, which is when the spark stops. Without the condenser, the spark will be of very short duration, and quite weak. The points will also arc on each opening, causing pitting of the contact surfaces and eventual breakdown.

Faults in the ignition system

Note: Voltages in the ignition circuit can be harmful, and painful! Do not touch connectors or components with the ignition on. Resistance testing of ignition components must be done with the fuse out and ignition switch off, and preferably with the component completely removed from the electrical circuit.

Testing of the condenser can be done by using a multimeter on the highest resistance (20M Ω - 20 Mohms) range. Take one of the bike electrical connections off the condenser, and connect the probes across the component, watching the meter display as you connect the probes. The meter should indicate a low initial resistance, with a rapid increase in resistance as the condenser charges over a period of a few seconds. The meter should, after no more than 5 seconds, indicate infinite resistance. If it shows some steady high resistance (eg 10Mohms), or slowly decreases after initially going high, the condenser needs to be replaced. Make sure your fingers aren’t touching the metal portion of the probes when you do this test, as it will give false readings. The ignition condensers can be tested in either polarity, with the same results. If reversing polarity immediately after a test, the initial meter reading may be false due to the charge on the condenser from the meter.

Coils can go faulty in a number of ways. The primary can go open circuit due to vibration or heat (continuous current for extended periods – burnout). The secondary can go open, or can short turns (a current path between layers of the winding, resulting in greatly reduced output), or a short to the outer case.

Testing of the coil is a 4 step process. First take all connections off the coil, including the high-tension lead (plug lead). Using a multimeter on low resistance range (200 Ω ), check the resistance between the two low tension (primary winding – 12 Volt) connectors. 6 volt coils should read around 2 to 2.5 ohms. 12 Volt coils should read between 4 and 5.5 ohms. If higher, it could be faulty or a higher voltage (eg 24v) coil. If lower, shorted turns are the most likely culprit – replace.

Next, check the secondary winding by a resistance (meter on 20K Ω range) check between the negative 12V terminal and the high-tension output (the brass connector inside the tower where the plug lead goes). This should be around 5 to 6 K Ω .

The last check is between either the negative terminal, or the high tension terminal, and the metal casing, with meter on highest Ω range. Should be infinite resistance from either point. Again, make sure your fingers aren’t touching the probes, as false reading will result. If not infinite resistance, the coil has a short to the case, and should be replaced.

Spark plug leads can be tested by checking resistance from end to end. Meter on 20K Ω range for Suppressor leads, or 200 Ω for copper core leads. For copper core high-tension leads, resistance should less than 1 Ω between the metal connectors at the ends. Radio frequency interference suppression leads can be identified by either reading the writing on the lead (it will say it’s “suppressor lead” or similar), or by taking the rubber boot off one end and looking where the lead enters the metal connector. Suppressor lead centre conductor looks like a number of strands of tiny fishing line coloured dark grey or black. Suppressor leads will measure around 5 K Ω for the approx 600 mm length. Any higher, they are possible faulty or the wrong type, and they start to limit the high-tension current to the point where the spark strength is degraded.

Similarly, spark plugs can be tested with a meter. Good idea to give the firing end of the plug a scrub with a brass or wire brush to remove any carbon or burnt oil deposits that could give a false reading. Suppressor plugs have an in-built resistor to limit the current of the high-tension system, thereby limiting the RF interference caused by the ignition system. Plugs without in-built resistor should read less than 1 Ω between the top cap (where the lead plugs on) and the centre electrode at the firing end. The suppressor plugs will read around 4 to 5 K Ω between top cap and the centre electrode. Both types should read infinite resistance between top cap or centre electrode and the metal casing. If in any doubt, replace the plugs – they’re fairly cheap.

Total suppressor resistance, from the coil end of the plug lead to the centre electrode at the firing end of the spark plug, should not exceed 5 K Ω . Any more than this and the spark may be weakened to the point where misfires or no spark could occur under normal operating conditions. Copper core plugs leads will give the more powerful spark, but may cause interference on nearby TV’s, radios, computer equipment, etc. If you use a computerised ignition system or other electronic equipment on your bike, use suppression leads or resistance plugs to a maximum of 5 K Ω resistance. It’s not a good idea to use both resistance plugs and suppressor leads together. One or the other will be fine for suppressing RFI.

Points can be checked by doing a resistance check from the point where the wire connects to the points to engine metal (ground/earth). Note that the other end of the points wire must be disconnected from the coil to do this test. 0 Ω for points closed, and infinite resistance for points open. Note that the condenser may still be in circuit (if it’s mounted on the points plate), so points open resistance reading may take a few seconds to reach infinite.

End-to-end testing.

If all components check out OK, a fault in the ignition system is most likely to be a bad connection or broken wire.

The following tests are done with the fuse in, and live 12 volts applied to the ignition system. For safety, take the spark plugs out and rest them on the head with leads still connected. This way, there’s no way the engine can start, and you can see if a spark occurs at the plug. Keep your hands and other body parts away from the electrical components and connectors. They get hurt if they get hit with ignition

voltages. Make sure you have no fuel or gas vapours in the vicinity, or fuel leaks. Have a fire extinguisher handy just in case.

Meter on 20V range. One lead on battery earth (positive terminal on older British bikes) or on a good bare metal part of engine or frame.

Ignition switch on, kill switch to run. Place the other meter probe on the power side of the coil primary (negative terminal on older bikes). Meter should read between 12.5 and 13.8 volts. If lower (eg 11 V), check state of battery. If no voltage reading, check the battery earth connection, then the fuse, then the ignition switch, then the kill switch, and the cables and connectors between all these components. You can use the meter probe to test for 12v along this route.

Once you have 12V at the power side of the coil primary, rotate the engine until the points are open. Measure voltage at the other primary connector on the coil (+ on older bikes) – should be 12V. If not, could be an open circuit coil, or a shorted condenser, or a short circuit to earth in the points cabling or points themselves. Most likely cause is the wire connection to the actual points being frayed or misaligned, or a missing insulator on the stud holding the points spring – the wire must connect to the points spring, but be insulated from the mounting stud. Follow through by turning the ignition off, and checking resistance of the coil primary, and the resistance between earth and the points wire.

Once you get 12V on both sides of the coil primary with points open, rotate the engine until the points close. You should now see 0 Volts on the points side of the coil primary (+ on older bikes). If not (ie still seeing greater than 0.2 volts), then there is either a broken wire or connector (open circuit) between the coil and the points, or the points are not closing properly. Points not closing will usually be caused by mechanical misalignment, or by an obstruction between the points contacts such as oil, dirt, corrosion, pitting/carbon, etc.

If all checks out OK, with fuse in, ignition on, kill switch to run, use the kickstarter to turn the engine over. Check for spark at the spark plug (still resting on the head). If no spark at all, check the plug lead and spark plugs as described previously.

A further check is the check for voltage at the plug end of the high-tension lead. Meter on 20V range, ignition on, points open, one meter probe on battery earth/frame. DO NOT kickstart, or close/open the points, or turn the power off, with meter connected to the plug lead, you will damage your meter. Disconnect the plug lead from the spark plug, and connect the other meter probe to the metal end of the lead. You should see around 10 to 12 V on the meter. If not, lead is faulty, or secondary winding of coil is open circuit. Check components as described previously, and replace as required.

Boyer Electronic Ignition Systems

Electronic ignition systems available for motorcycles usually just replace the points, with some added electronics to provide for spark advance. They still require coils to generate the high-tension voltage for spark.

Diagram 2 shows a typical Boyer setup, using 2 coils.

The Boyer control box has 5 connections.

1. The -12 volt power input line - White2. The -12 volt coil power output line - Black3. The +12 volt line – Red4. One pickup sensor line – Black/ yellow5. The other pickup sensor line. – Black/white

Boyer control boxes need an absolute minimum of 10 volts to operate. If your battery is not well charged, and able to supply 10 volts under load (ie with ignition on), the unit will not operate.

Power is applied to the control unit once the ignition switch is turned on, and the kill switch is in run. Power will not be applied to the coils until the first pulse is received from the pickup sensor unit, which is mounted where the points used to go and using the points wires to connect the pickup sensor unit to the control box. If pulses stop being sent from the pickup sensor, the power to the coils will be cut off approximately 10 seconds later. This is to stop coils being overheated and burnt out, and batteries being flattened, by continuously feeding power to the coils when it is not required.

Note that the coils are wired in series. That means the current path goes from the Boyer control box, through one coil, then through the other coil, and then to earth. Wiring coils in parallel will cause damage to the control box due to excess current. The control box will limit the coil(s) primary winding voltage to 400V, with two coils wired in series, this equates to 200 volts per coil. Depending on the coils used, this limiting may result in limited output voltage to the spark plugs. Converting to 2 x 6v coils gets around this possible problem – something to think about if you’re getting

Battery

FuseIgn Sw Kill Sw

Coil

SparkPlug

DIAGRAM 2

Current Flow

Coil

Pickup Plate

Boyer

White

Black

Black

Red

Black/YellowBlack/White

weak spark with a Boyer and 2 x 12v coils. Some people prefer a single 12v coil with dual high-tension outputs.

Boyers fire both cylinders at once, at both the top of the compression stroke (when it should happen), and at the top of the exhaust stroke (when it’s not required, but doesn’t hurt). This makes the design simpler, and also assures matched ignition timing between twin cylinders. The pickup sensor is simply two coils wired in series, and mounted 180 degrees apart, with their centre metal cores protruding. Magnets are similarly set onto a rotor fitted to the camshaft. As the rotor rotates, the magnets sweep close by the protruding metal cores, which induces a voltage in the coils. This voltage pulse is fed to the control box via two wires, and is used to “trigger” the momentary disconnection of the negative power line from the ignition coils (virtually the same as opening the points), creating spark.

When initially set up, the pickup sensor is timed at full ignition advance. When the engine is running at idle, the spark is electronically retarded by approximately 10 degrees. As the engine speed increases, less retardation is applied, creating more advance. Maximum advance (or more precisely zero retardation) is reached around 5,000 RPM. Condensers are not required in a Boyer setup.

Note that if the pickup sensor cable are wired in reverse, the pulse recived will be the wrong polarity, and the control unit will actually sense the trigger pulse when the magnets are leaving the pickups coils, rather than as they approach. This has the effect of significantly retarding the spark (by around 50 degrees), and the engine will be virtually impossible to start. You will see spark, and everything will look good, but the timing will be way off. Make sure you get the polarities right from the sensor to the control box for the black/yellow and black/white wires.

Fault-finding a Boyer setup

Note that the fault-finding methods described here are for a positive earth bike, with two coils.

Boyer control boxes need an absolute minimum of 10 volts to operate. If the battery is not well charged, and able to supply at least 11.0 volts under load (ie. with ignition on), the unit may not operate properly. Make sure you have a good battery in place before doing any other fault finding.

Check the 12v power side by meter on 20V range, connecting one probe to battery earth. Connect the other probe to the primary winding (12V) connector on the first coil that has the black power wire from the Boyer. Take the spark plugs out and rest them on the head with leads still connected. With ignition and kill switches on, rotate the engine with the kickstarter. After 1 or 2 revolutions of the engine, you should see 12v on the meter. This will return to zero volts after 10 seconds or so, so watch carefully.

Now check the pickup sensor. Take both the black/yellow and black/white wires out of their connections to the Boyer control box. With meter on 200 Ω range, measure the resistance between these to wires going to the sensor plate. You should read 132 Ω. If significantly lower than 132 Ω , one of the sensor coils may be shorted, or the

printed circuit board that the coils are mounted on may have a short between tracks. If significantly more than 132 Ω, or infinite resistance, there is probably a faulty connector between the control box and the pickup sensor. Check the resistance of each wire from end-to-end individually, and check the resistance of the sensor at the connector on the senor plate itself.

The last check you need to make is the wiring of the coils. With meter on 200 Ω, and ignition off, check the resistance from the -12V primary connector on the first coil, to the +12V connector on the other coil – that’s means across both coil primaries. For 2 x 12V coils connected in series, you should read no more than 10 Ω . For 1 x double ended 12V coil, or for 2 x 6V coils, you should read no more than 5 Ω . If more, it’s most likely the wire joining the two coils together, but could also be a faulty primary winding on either coil.

If the power connections, coils connections, and the sensor checks above check out OK, and you’re sure of the good state of the battery, the fault will probably be with the control box. If it’s just been fitted, and not yet worked at all, check that the right connections are being made to the control box, as per the Boyer instructions.

As mentioned previously, you should have no more than 5 K Ω total resistance on each plug lead / resistor spark plug combination.

2. Other Electrical Systems

This section covers the electrical systems on the bike such as:

Charging system Lighting system Warning system

Charging system

The charging system on the Meriden Triumphs is quite simple. An alternator, a rectifier, and a zener diode, along with the battery of course.

The alternator has two parts. A rotor, which is basically a strong magnetised cylinder mounted on the outer end of the crankshaft, and a stator, which is a ring of coils on a “donut-shaped” iron core, mounted around the rotor. As the magnetised rotor is rotated by the engine, its magnetic field “cuts through” the winding of the coils, producing a voltage in the coil. Because of the rotation, and the north/south poles of the magnet, the voltage alternates between positive and negative. When an electrical load is applied and current flows, it is called alternating current, or AC (also why it’s called an alternator).

To be useful in a direct current (DC) environment such as bike electrics, this alternating current must be changed (rectified) to direct current. This is the job of the rectifier. The rectifier is basically 4 high current diodes wired in a Bridge Rectifier

pattern, which converts the positive/negative AC voltage from the alternator to all-positive or all-negative voltage.

Extra-Technical Information

Diagram 3 shows a typical bridge rectifier setup and corresponding waveforms. Please note that I use the “electron flow” theory to explain operation.

Diodes only pass current in one direction – think of it as the current being able to go up the “slope” of a diode, but not up the “cliff”. Looking at Diagram 3 above, when the AC voltage is fed to the input, in one half of the AC cycle current is passed by the top left and bottom right diodes, while the other two diodes are reverse biased and pass no current. In the other half cycle, the top right and bottom left diodes are the ones forward biased and passing current, while the other two are blocking current flow. This results in a Direct Current (DC) output made up of both the positive and negative halves of the AC input.

Note that the older style rectifiers use the mounting bolt as the earth connection for the positive DC output.

Fault finding bridge rectifiers

To test a bridge rectifier, the easiest way is to use a multimeter with a diode checker. This will be indicated by a certain switch position on the meter, or a combination of switches, showing the diode symbol. In this mode, the meter will show the voltage drop across a forward biased diode, therefore the position of the probes is important when checking diodes.

To eradicate the possibility of either the alternator or the rest of the bike electrics affecting your testing, take the fuse out, and remove all the wires connecting to the rectifier. Be careful to note which wires go where – you don’t want to put them back in the wrong place or you’ll end up cooking some wiring.

You have 8 checks to do – forward and reverse on each diode in the set of 4.

-15

AC input from alternator DC output

-15

0

+150

DIAGRAM 3

Using diagram 3 above as an example, the first test would be putting the red probe on the negative output connector, and the black probe on either AC input connector. This will forward bias one of the left hand diodes, and you should read between .400 and .700 on the meter. Test the other left hand diode by moving the black probe to the other AC input connector. Reading should be very similar. Now reverse the two probes so the black is on the negative output connector, and the red probe is on either AC input connector. You should read infinite – “1” then blank on an LCD screen multimeter. Swap the red probe to the other AC input connector to check the other diode.

Now test the right hand diodes by placing the black probe on the positive DC output connector (may be the centre bolt/earth on the older rectifiers), and the red on either AC input connector. Again, you should see .400 to .700 on the meter. Check the other diode by swapping the red probe to the other AC input connector. Now check the reverse bias by placing the red probe on the positive DC output, and the black probe on either AC input. You should see “1” then blank on the meter.

If at any stage during this testing, you see something like “.003” or any similar low reading, it means the diode being tested is faulty. The same diode will probably measure the same in the reverse test, as it’s burnt out and imitating a piece of charcoal. If this is the case, it’s time to replace the whole rectifier.

Tip is to go to the local electronics shop and buy a 20A bridge rectifier for $5, and fit it to an L bracket. Connections are the same, except you might have to wire the positive (if system is positive earth) DC output to earth – the L bracket.

Zener Diode

The symbol for a Zener diode is shown here.

The Zener diode is basically a rudimentary voltage regulator, and is used the stop the alternator voltage getting high enough to cause damage to the battery, lighting globes, coils, etc.

The zener is special in the sense that it acts as a normal diode in the forward biased state (as explained in the Rectifier section – current can flow up the slope but not up the cliff), but in the reversed biased state it will only block current until a certain pre-set limit is reached, and then it will conduct. This limit on 12 volt bikes is set at 15.0V. Zeners used as voltage regulators are wired in reverse bias mode, and have high current and high power dissipation characteristics. Zeners will have either a finned heatsink, or be mounted on metal in an area of high air flow.

Extra-technical information

As alternator rotor speed increases, the magnetic lines of force cutting the windings of the stator increase in frequency. This not only increases the frequency of the AC output, but also the output voltage (amplitude). To protect electrical components, such as the battery from overcharging, and the light globes from blowing, the voltage must be controlled.

As can be seen in diagram 4 above (positive earth system), the AC output of the alternator is applied to the rectifier, which converts the AC to DC. This DC is then applied to the battery and the rest of the electrical system of the bike. The Zener is wired in reverse bias across the main power feed out of the rectifier.

When the voltage at the output of the rectifier is less than 15 volts, the Zener is inactive, and has no affect on the rest of the electrical system. If the DC voltage on the anode (the “cliff” side) of the zener reaches the preset trigger voltage (15.0V) the Zener diode immediately goes into the avalanche condition, and provides a very low resistance path to earth – almost a dead short circuit. Current flows through the Zener to earth. This has the effect of rapidly reducing the voltage coming out of the rectifier. As the voltage goes below 15 volts, the Zener goes back to passive state. Thus, the voltage coming out of the rectifier is limited to a maximum of 15 volts.

Testing a Zener

The simplest test you can do on a Zener diode is to check it with a multimeter in diode test mode. It will act as a normal diode with the test voltage available through the multimeter. It should show 0.400 to 0.600 on the meter when forward biased, and “1 blank” in reverse bias. For Zeners meant for positive earth systems, the base stud or heatsink will be the cathode (the pointy end of the triangle symbol), and the insulated blade connector will be the anode( the flat end of the triangle – the “cliff” face).

The wire from the battery/rectifier should be disconnected. It’s OK to leave the Zener mounted, as long as you can find a bare metal earth point to put your probe on. Multimeter in diode test mode.

For positive earth systems: Red probe on Zener blade, black on earth - .4 to .6 reading. Red on earth, black on blade – 1 blank reading.

ZenerAlternator

Rectifier

Battery

DIAGRAM 4

Rest of bike electrical load

For negative earth systems: Red on earth, black on Zener connector - .4 to.6 volts, Red on connector, black on earth – 1 Blank reading.

If the Zener is faulty, it will usually show up as a short circuit (low readings in both directions), and other problems with bike electrics will be quite evident – constantly blowing fuses will be the main symptom.

To test the reverse turn on voltage of the Zener, use the following test circuit. Please note this is for Positive earth systems – Zeners with the cathode being the base mounting stud or heatsink.

See diagram 5.

Wire two standard 9 volt batteries in series as shown – positive of one to the negative of the other. These are the standard batteries that go into toys, smoke detectors, multimeters, etc. In this test, it’s likely you will drain a fair bit of power out of them, so if you have to go and buy some, get the cheapest you can find.

Once the batteries are wired together, use your multimeter on 20V DC range to make sure the combined voltage is above 15 Volts.

Using a piece of wire, connect the stud or heatsink of the Zener to the positive battery point, and also wire to the red probe of the multimeter. Using another piece of wire, connect the negative battery terminal to the black meter probe. With meter on 20V DC range, you should see around 18-19 volts.

Now touch the black probe (with wire still attached) to the blade connector on the zener. You should see the voltage drop down to 15 volts straight away. Don’t leave it there very long – 2 or 3 seconds should be heaps. The internal resistance of the batteries will limit the current, but the wires may still get warm or hot.

18.50

DIAGRAM 5

If it goes below 15 volts (eg 1 or 2), you either have the diode forward biased (reverse the connections on the zener) or it’s faulty (do the previous simple multimeter diode test). If this is the case, the wires will get hot really quickly, and the batteries may also get very hot if the probe is left on the Zener too long. This is why I’ve suggested to just touch the probe on, and not wire it to the batteries – easier and quicker to remove.

If the voltage doesn’t come down from 18 to 15 volts, the Zener could be open circuit (check your test connections, and do the simple diode test).

Alternator

Two basic types of alternator may be fitted to your bike; A single phase alternator, or a 3 phase alternator. It’s pretty simple to tell which you have. Take a look at the wires and connectors coming out of the lead coming from the alternator. If you have two wires coming from the alternator, you have a single phase system. If you have 3 wires coming from the alternator, you have a 3 phase system. The 3 phase systems require a special 6-diode rectifier pack, and puts out a slightly higher current than the single phase system.

The two basic parameters affecting alternator performance are the strength of the rotor magnet, and the speed of rotation of the rotor. The stronger the magnet, the greater the voltage developed across the stator windings, and therefore the greater the current capability. Maximum output current for a single phase alternator in new condition is approximately 9 amps. Magnets will lose some of their magnetism over time, because of mechanical shock and heat, thus reducing the output capability.

The windings of the stator do not usually degrade in terms of performance, but can be affected by knocks during maintenance, or shorted turns due to insulation breakdown over an extended time.

Testing the Alternator stator

There are two fairly simple tests for the alternator stator, both done with a multimeter.

Disconnect the cables coming out of the alternator, where they connect into the loom. Note which wire goes where before you pull them apart.

Now with the multimeter on the lowest resistance range (200 Ω), test the continuity between the two wires coming from the alternator – you should see around 1Ω . If more, you have a faulty wire or connector in the lead coming from the alternator, or a faulty stator (rare but possible).

Now check the insulation from the stator to earth. Multimeter on highest resistance range (eg 20M Ω), and measure between one of the alternator wires and earth, should read infinite (“1” then blank on the meter). Do not have you fingers on any probe metal parts, as this will give a false reading. If not infinite resistance, the stator could have a short to earth via the metal core, or the cable could be broken and touching the engine casing.

Battery

The standard battery for the older triumphs is of the lead/acid variety, with a rating of 12 volts and 8-9 amp/hours. Some owners prefer to replace the lead/acid type with Absorbed Glass Mat (AGM) maintenance free type. They still contain acid, but have no drainage tube, are less susceptible to the affects of vibration, and have the same charging characteristics as the standard lead/acid batteries. They are smaller in size for the same amp/hour capacity, so fitting may present some issues (eg. Battery movement in the battery carrier cradle). Gel Cell batteries are not really suitable for these bikes, as significant modification to the charging system is required to limit the charge current to the battery. Fitting a Gel Cell to a bike with a standard charging system will significantly shorten the life of the Gel Cell.

There are several tests that can be done on the battery, such as specific gravity of the electrolyte (liquid) with a hydrometer, fluid level, standing voltage, etc. but by far the most effective test that can be simply achieved is the “voltage under load” test.

To do this test, first connect the multimeter on 20V range directly across the battery, and read the voltage with ignition off and all lights off. A fully charged battery will read pretty close to 12.8V. A 50% charged battery will read 12.2V with no load, and a discharged battery will read 11.9V with no load. Make sure the battery is fully charged before doing the load test. Motorcycle batteries should be charged at a rate of no more than 1 amp. High charge-rate car battery chargers are not suitable for motorcycle batteries, as their charge rate can be as high as 10-12 amps – this level of charge will boil the motorcycle battery.

Now turn the headlight on low beam. This will draw approximately 4 amps out of the battery. The battery voltage will drop to about 12.2 volts as soon as you turn the headlight on. Keep an eye on the voltage reading for a full 3 minutes. If it falls below 10 Volts, your battery is faulty, and needs to be replaced. If the voltage drops to 11 volts, the battery is weak, and you need to consider refurbishment or replacement. A good battery will read around 11.9 to 12.2 volts after 3 minutes. Switch the headlight off, and after two minutes check the reading again. That battery voltage should have crept back up to around 12.6 to 12.7 volts. If so, your battery is in good condition.

End-to-end Charging system testing

If you are satisfied that all the charging system components are in good condition, you then need to check the overall system operation.

The two basic checks to do for end-to-end testing the charging system are:

Check the battery voltage with the engine running around 2000 rpm – should read around 13.7 to 14.2 volts. If down at 12 volts, you have a problem with one or more of the charging system components, or cabling/connections between them.

In a shaded area, locate the bike near a wall or similar, so the headlight will shine on the wall and you can readily see the light pattern. With engine running at idle, turn the headlight on high beam. Engine revs may drop a little

(good, because the alternator is loading the engine). Rev the engine to 2000 rpm, and the headlight should get slightly brighter when the revs are up. This indicates that the alternator and rectifier are working. Lower the revs and the light should go slightly dimmer. If the light does not go brighter with revs above idle, perform the previous test for battery voltage at revs.

Indicators

The wiring for indicators is basically as illustrated in Diagram 6. Note that the return current path is via the ground/earth mounting of the indicator arms. Some after-market indicators do not make good earth contact at the mounting points, and may require star lock washers, or special extra wiring, to ensure a good earth.

The indicator system is made up of four basic components; the indicator switch, the flasher unit (aka flasher can), the indicator lights themselves, and the indicator warning lamp.

Battery

Fuse

Ign Sw

DIAGRAM 6

Left Hand Side

RightHand Side

Indicator Switch (handlebar)

Flasher Can

Warning lamp

DIAGRAM 7

a) rest b) activated

The flasher unit, or flasher can, consists of two metal strips, one being plain metal with a contact at the end, and the other being two strips of dissimilar metals bonded together, again with a contact at the end. The bi-metal strip is surrounded by a heating element. When current passes through the heating element, through the contacts and along the plain strip (Diagram 7a), the bimetal strip is heated and bends (due to the different rates of expansion of the two dissimilar metals) (Diagram 7b). This breaks the contacts apart, current stops flowing, the heater elements no longer heats, and the bi-metal strip returns to it’s original position (a). The contacts make, current flows, heater heats, bi-metal strip bends, contacts break (b), and the cycle continues until current is stopped externally (switched off).

This simple heat-based on/off switching method also allows you to see when an indicator main (front or rear) globe is blown by the quicker flash rate with a lower load. With one globe open circuit, there will only be half the current flowing. The heater heats the bi-metal strip to half the extent, the bi-metal strip bends to the point of just opening the contacts, and the bi-metal strip takes less time to straighten up again after the current is broken by the contacts opening. Similarly, if your battery voltage is low, the heater takes a long time to heat the bi-metal strip, and the indicator lamps will stay on longer, and will have a shorter off time.

The indicator warning lamp (in the headlamp nacelle) works on the principle of a high resistance vs low resistance voltage divider. When 12V is applied to one side of the indicator system, and the lights on that side are on, 12V is also applied to one side of the warning lamp. The other side of the warning lamp is connected to earth via the filaments in the other side indicators. With it’s low wattage and therefore higher resistance, the main voltage is dropped across the warning lamp. A small amount of current actually flows though the other side filaments, but no enough to make them glow.

Lighting System

The lighting system is again fairly simple. The battery and charging system in combination are the source of current for the lighting system, and earth returns via the frame are common, although the main lamps have their own earth wire.

The lighting switch will normally have 3 positions – Off, Parking Lamps (aka Safety Lighting), and Main. The headlight beam also has a control switch mounted on the handlebar, switching between low and high beam.

There are two possible ways to have the lighting power routed. One is straight from the battery via the fuse, and the other is to have the lights only available when the ignition switch is on. Both have pro’s and con’s, and it’s really up to the individual owner as to which way works best for them.

Faults in the lighting system

The majority of faults in the lighting system are either globes blowing (filament going open circuit), or bad connections.

Globes blowing will usually be caused by: poor quality globes being affected by vibration excessive vibration through worn or brittle mountings excessive voltage (open circuit or disconnected Zener) filament age – if they built them to last forever, you’d never buy any more…

Bad connections can be caused by: vibration – connectors coming apart Cable movement – broken conductors inside the insulation due to constant

bending Corrosion – due to age, or connections being exposed to the weather or

corrosive elements (eg battery acid, fuel vapour, cleaning agents, etc) Poor earth connections due to attachment to frame with paintwork.

The fault finding routine for the lighting system is as follows:

If all lights don’t work:

1. Check fuse and battery are in good condition. Check the fuse with a multimeter on low resistance range. Even though it might look OK, it may be broken near an end under the cap.

2. Fault is likely to be the lighting switch or a bad connection to or from it. If lights are wired only to come on with the ignition switch on, check the ignition switch as well.

If it’s an individual light (not all of them) that’s not working:

3. Check the globe. Either testing it in another known-good socket, or testing it with the multimeter on resistance range. Sometimes you can see the filament flopping around inside the glass, or grey/black stains on the inside of the glass, signifying the filament is blown. White stains on the inside of the globe signify that air has gotten inside the globe, and the filament has blown and burnt the oxygen.

4. If the globe is not the problem, check the earth connection for the socket. With the fuse out, check for continuity between the earth side of the socket and battery earth. Multimeter on low resistance range (200 Ω ). If less than 1 or 2 ohms, move to next step. If more than 1 or 2 ohms, start checking the cabling, connectors, and any earth attachment points backwards towards the battery from the socket.

5. If globe and earth are OK, put the fuse back in and, with multimeter on 20V range, start checking the power through the cabling and switches. A good place to start is inside the headlamp shell (most lighting power routes through this area. Check the connectors on the back of the lighting switch for 12V from the battery, then work your way forward to the socket that doesn’t work.

Horn

The horn is a fairly simple electro-mechanical device that uses a switched electromagnet to vibrate a plate, creating sound waves.

Diagram 8 depicts a simple horn construction.

When power is first applied (you press the horn button), the electromagnet energises, and draws the steel vibrating plate towards it’s core. This causes a rod mounted on the underside of the vibrating plate to break the electrical contacts apart, and current stops flowing through the electromagnet. The steel vibrating plate snaps back to it’s rest position, and the electrical contact meet and again allow current to flow through the electromagnet. This cycle continues until the current is switched off externally (ie you stop pressing the horn button). The vibration of the plate is at such a frequency as to create sound waves.

Most horns have an adjustment screw on the rear of the case to adjust the tone of the horn. This screw merely adjusts the position of the upper contact, thus changing the amount of movement of the vibrating plate required to make/break the contact.

Fault finding a horn

The horn is most likely to break down due to three causes: Internal corrosion due to exposure to the weather – usually caused by the

breakdown of sealing materials around the case and vibrating plate. Maladjustment or misalignment of the contacts, due to the adjustment screw

moving with vibration. Broken cabling and poor connections to the horn and horn switch.

To test the horn, take the wires off the horn connectors (note which way they go), and using a multimeter on resistance range, check for resistance between the two connectors on the horn casing. You should see around 16 or 20 Ω . If infinite resistance, you can try rotating the adjustment screw on the back of the casing until you get a reading. Most likely you’ll need to take it apart. Take note of which way the plate and the case are oriented together – a couple of dots of liquid paper can help align when putting it back together. Take the plate off, and check the internal connection and contacts, as well as the position of the adjustment screw. Remember

Vibrating plate

Electromagnet

Contacts

Casing

DIAGRAM 8

to seal the case against the weather – if a gasket is not available, use a thin bead of silicon.

Remember, you should have a low resistance reading when the horn is not operating. If the adjustment screw is adjusted correctly, you should be able to press on the vibrating plate by using fingers, and cause the contacts to break the connection, making the meter read infinite resistance. Let the plate go, and the reading should return to low resistance.

Connect up the power and earth cables, and test. Then adjust the screw to give the tone you require. Be aware that the more the plate has to move (the lower the tone), the more average power will be required to operate the horn.

If, when you connect it all back up and press the horn button, you just hear a click when you press the horn button, and another when you let it go, the adjustment screw is maladjusted, and the vibrating plate is not breaking the contacts.

P.S.Hopefully this information will help someone to keep their Triumph running and safe. Please feel free to use it as a guide, but remember many of the older bikes have gone through many owners, and thus may be fitted with many different components.

If you have any comments or suggestions for future versions, please drop me a line using the TriumphRat.net PM system.

Pete.