General Information

Suitable instruments for fault diagnosis of the electrical system in the car are a diagnostics tool, a voltmeter and an ohmmeter.
^ When checking voltage in a circuit, use the diagnostics tool or a voltmeter.
If the voltmeter is of analogue type, it should have an internal resistance of at least 20 M ohm/Volt.
^ When checking resistance in circuits, use the diagnostics tool or an ohmmeter.
The ohmmeter must not be used for checking components that contain semi-conductors, e.g. electronic control modules and relays with time- delay functions, 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 there is no current already flowing through the circuit and that a correct reading will be obtained.