FAULT FINDING - General (Wiring diagrams)

FAULT FINDING - General

The following general points on fault finding should be observed at all times.

• Check the circuit fuses.
• Check the battery for state of charge and clean and tight connections.
• Check alternator belt tension.
• DO NOT start removing or replacing components until the fault has been positively identified.
• Familiarise yourself with the circuit diagram of the affected system.
• Where other systems share the same circuit, check their function to verify the extent of the problem. If shared systems operate, the indications are that the fault is confined to the one circuit.
• Test for the most likely cause first based on the symptoms and how the system operates.
• Use the appropriate test equipment.
• Always carry out a full functional check of the system after repair including any other system that shares the same fuses or earths.

Test equipment

TestBook and Microcheck

Always follow precisely the instructions shown on the display.

Test Lamp

CAUTION: Do not use a test lamp on a circuit containing solid-state components as damage to the solid-state components may occur. Always use a multimeter of 10 megaohms or higher impedance to test circuits containing solid-state components.

Test lamps with a 12v bulb, can be used to check circuits without solid-state components to verify that voltage is present.

Voltmeter

In addition to confirming that voltage is present at a particular point in a circuit, the reading obtained, when compared with the battery or alternator output voltage, will indicate the volt drop of the wiring and components in that part of the circuit.

Ohm-meter

Use an ohm-meter to check circuits for continuity and to measure the resistance in part or all of a circuit.

When taking resistance readings on a circuit containing diodes or solid-state components, take a reading then reverse the test leads and compare the result. False ohm-meter reading can sometimes occur where diodes or solid-state components are connected in a circuit.

Testing

Always observe the following when carrying out fault finding tests:

• Follow precisely the instructions provided with the test instrument or equipment.
• It is not necessary to disconnect a connector to check for continuity or voltage, use a test probe in the back of the connector.
• Always check from both sides of a connector to ensure that dirt, corrosion or poor contact of the pins is not the cause of an open circuit, poor or intermittent continuity or a high resistance in the circuit.