Diagnostic Aids

Fault Diagnosis

When diagnosing an electrical fault, follow the steps below:
1 Read the circuit description appropriate to the reported fault to ensure a good understanding of circuit operation.
2 Study the power distribution, fuse details and earth distribution diagrams and identify other circuits which share fuses and/or earth points. Check whether these circuits operate correctly.
3 Using the photographs contained in the Connector section, locate a point on the circuit (approximately half way between supply and earth) which is easily accessible.
4 Check that the pin-out details of the connector are correct and that the correct signals exist at the correct terminals.
5 Using the marker pen supplied (or other suitable non-permanent marker pen), mark the parts of the circuit you have verified.
6 Continue to the next point on the circuit which is easiest to access and repeat the above.
7 Continue with this approach until a fault is found, rectify the fault and then verify that the circuit operates correctly.

CAUTION: Never probe directly into the front face of a connector. This can damage the terminal and cause a failure. Always probe the back of a terminal, taking care not to damage the terminal or any seals.

Never probe wire insulation. On small diameter cables this can cut the conductors. It may also allow moisture into the cable, causing corrosion.