When it comes to trouble shooting an electrical circuit one of the most simple tests is the continuity test. The name of the test implies what the test does, it tests for a continuous circuit, meaning that nothing is broken or open in the wire or the circuit. All wires and circuits have a certain amount of resistance associated with them depending on the size of the wires, the length of the wire and the material of the wire or circuit.
For safety, disconnect the power supply to any electrical circuit that you are working on.
Turn the dial on the multimeter to the indicator marked "ohms" to test for resistance. A continuity test is actually a test for the amount of resistance in a circuit or, more precisely, that resistance exists and there is not an open or broken circuit. The multimeter has two test lead wires on it that look like ballpoint pens. The red is the positive side; the black is the common side.
Place the end of each test lead of the multimeter at each end of the wire or circuit to determine if there is an indication of resistance. If there is resistance in the wire, then the continuity test is positive and will show a value on the multimeter. If the amount of resistance shows zero, then the wire or circuit is open or broken.
Make sure that you are testing a circuit or wire that is intended to be a closed loop.
Never work on wires or circuits that have electric power in them.