General

Suitable instruments for diagnosing faults in the car's electrical system are a diagnostic tool, a voltmeter and an ohmmeter.

^ Use a diagnostic tool or voltmeter to measure voltages in a circuit.
^ If the voltmeter is analogue, it should have an internal resistance of at least 20 M ohm/Volt.
^ Use a diagnostic tool or ohmmeter to measure the resistance of a circuit.
^ The ohmmeter must not be used for taking readings of components containing semiconductors, e.g. control modules and time-delay relays, etc.
^ When measuring resistance, the voltage supply to the system being tested must be disconnected as the test instrument feeds a small current into the circuit being tested.
^ This will ensure that no current is already flowing through the circuit and that a correct reading will be obtained.