Electrical System Fault Diagnosis - Checking for Voltage in the Circuit

Checking for voltage is one of the standard checks when any current-consuming device fails. Connect one lead of the circuit tester or voltmeter to the negative battery terminal or to any securely grounded point on the chassis/engine. Connect the other lead to the terminal connection of the circuit being tested, preferably the one closest to the battery or fuse. Turn on power to the circuit. Remember that some circuits are powered only in certain ignition switch positions. If voltage is present (the tester lamp lights up or the voltmeter shows a reading), the section of circuit between the tested terminal connection and the battery is good.

Continue the check in the same way, moving from one terminal connection of the circuit to the next, working away from the battery/fuse. The faulty section of the circuit will be located between the point where the tester shows no voltage and the previously tested good terminal connection. The most common cause of failure is an open in the wiring, or corrosion/looseness of the terminal connection.