Electrical

•Electricity

•Fuses

•Relays

•Solenoids

•Electrical Testing

•Wiring Harnesses•Testing•Voltage Drop Testing•Test Procedures

•Cables/Connections•Glow Plugs

• The flow of electrons from atom to atom in a conductor

• Electricity is based on a theory- an “unseen” force because the energy itself cannot be seen, heard, touched, or smelled

What is Electricity?

Fuses- devices used to protect the electrical circuit from too much current flow

•A fuse is designed to open the circuit when the

current reaches a predetermined level.

•Fuses are rated in Amps

•Do not install a fuse larger than is designed for

the circuit

Why Use Relays?

•To direct electricity to a high current device like a

starter motor, with the use of a light duty switch

(key switch)

•To control devices

-A relay is a switch that changes states when voltage

is applied to its input. The input connects to an electric

coil. When voltage is replaced across the input, the coil

magnetizes and moves a switch contact.

•Relay we use has a single switch that is normally open

(N.O.)- refers to the effect of the switch in its normal

(non-energized state)

Electric symbol we use for these relays - the symbol shows the coiland switch

Why Use Relays?

8530

868787A

-When the coil is not energized a spring keeps the switch

held open or OFF. When the coil is energized the magnetic

field pulls the switch against the normally open contact

thereby closing the switch.

Starter motor solenoid or magnetic switch

– Consists of a contact plate, plunger, plunger shaft,

pull-in coil, hold in coil and return spring

-When power is applied to coil terminal (key turned to start), current

flows through pull in and hold in coils. Magnetic field pulls in plunger

(the end of plunger has a contact disc). Disc makes contact with the

two main contacts and an R terminal contact. Battery is connected to

one main contact and the starter motor is connected to the other.

Current flows between the battery and starter motor. Current also

bypasses the pull in coil. The hold in coil continues to keep the solenoid

energized until the key switch is opened. At that instant current no longer

flows through the hold in coil and the contact disc is spring returned and

starter motor quits turning.

When voltage is placed across ends of coil, coil

magnetizes (magnetism moves a plunger)

Cut away view of coil commonly found on hydraulic

control valves

–Solenoids often take the place of what use to be done by mechanical

linkages, levers and switches.

-Common uses for solenoids are to control mechanical, hydraulic and

electric circuits.

Solenoid- a coil of wire

•Sensors (referred to as senders) - devices that respond

to a physical “stimulus”

•Variable Resistive Sensors - as physical property

changes, resistance of sensor changes

•Variable Capacitance Sensors - (engine oil pressure and

hydraulic oil charge pressure)–three wires to these sensors: ground lead, supply voltage lead

and sensor signal–Variable Capacitance sensors- have a circuit built into them.

The circuit converts the capacitance to an output voltage proportional

to the pressure. As the pressure increases the voltage increases.

Sensors

Switch sensors (air filter and hydraulic filter)–close or open when the physical property reaches

predetermined level

Sensors

Testing

•Harnesses - Suspected defect in a wire–test for continuity with an ohm meter–after checking for continuity, check for a short to nearby

pins, battery ground and battery positive

•Switches - Test leads on correct pins–With wires disconnected from the switch, connect ohm

meter across the switch–Switch can often be tested with a voltmeter in a live circuit

-With the switch open you should read infinite ohms. With the switch

closed you should read zero ohms. Anything other than these

readings indicates a faulty switch.

•Relays - Test activation signal–May be able to test for activation signal by listening to

the relay–Test switch output

–same test for any other switch–activate the relay and check that the switch functions

properly-Activation Signal- When activated and or deactivated, many relays make a

clicking sound. If the clicking sound is present, you can generally assume that

the activation signal is present. A more positive method is to check for ground

and the correct activation signal at the relay using a volt meter. If you do not

have the activation signal, the relay coil was shorted and should be replaced.

If you do not have the activation signal, the cause for this must be found.

Testing

Testing

Relays – Quick Testing Tips

•Replace relay with a known good relay• quick and effective

•Remove relay and put a jumper across correct pins to

simulate a closed switch–if output circuit functions, the circuit is ok

•Modules / Controllers

•First, check for correct ground and power to module

•If a known good module is available, replacement is

the best test

•Observe symptoms

•Often controllers are expensive–casual controller replacement is not recommended

-Because modules often are complex internally and perform many

functions, it can be difficult to determine if a problem exists.

Testing

Voltage Drop Testing

•Voltage drop- the difference in voltage potential when

measured across a circuit or component creating resistance-Voltage Drop- “Resistance decreases the amount of voltage available.”

•Resistance- an opposing force, created by a circuit or

component, to the flow of electrical current-Resistance- “There is a small amount of natural resistance when voltage

flow through wires, switches, grounds or connections. The resistance

increases beyond acceptable limits if corrosion develops, fittings become

loose or wires fray. Resistance increases each time something, such as a

wire, a switch, connections, or the ground are added to the circuit.”

What Else Should be Tested

–Each wire, ground, connector, switch, solenoid and the

complete circuit should be tested–Each connection point is a potential source of increased

resistance