Multimeters are used to measure various electrical properties of a circuit.
There are two types of displays on multimeters: digital and analog. Digital multimeters are useful for getting exact values, but only update a few times a second, thus making it difficult to catch quick changes. Analog multimeters are more difficult to read precise values from, but update immediately on a change, making them useful when tracking down a short or similar transient event by watching for the needle to jump. In both styles of multimeter, the circuit is tested by setting the multimeter to the correct mode and attaching the leads to the circuit.
Multimeters often have a variety of features, but two are of particular use in automotive work:
- DC Voltmeter. This shows the voltage of a circuit. The positive lead is attached to a positive source, usually the battery, the exposed end of a wire or connector, a relay or a fuse, while the negative lead is connected to ground, which may simply be the body of the car.
- Amp Meter. This shows how many amps the circuit is drawing. The leads must be connected in line with the circuit. For example, to test the amount of amps drawn at the battery, you need to disconnect one of the wires from the battery, connecting one lead to the battery terminal and the other lead to the wire.