Electrical circuits require voltage to operate the components connected to the specific circuit. So if there is no voltage, there is no function. When troubleshooting electrical problems, it is good to check for voltage at the load point in the circuit.

The load point is the element that the circuit provides power to.  It could be a light bulb, wiper motor, blower motor, etc. The load point can be checked with a voltmeter or a 12-volt test light. A voltmeter is the better choice because it will give you an exact voltage reading, although a test light will work fine for performing quick voltage checks.

If there is no voltage found at the load point, you should first check the fuse, fuse link or circuit breaker that protects the circuit, or the power relay that supplies voltage to the circuit.

If the problem is a blown fuse, replacing the fuse may restore power temporarily, but unless the underlying cause for the overload is found and corrected, your “fix” probably will not last. Whatever you do, do not substitute a fuse of greater capacity! A larger fuse may be able to handle a greater load but the wiring and the rest of the circuit cannot. A circuit designed for a 10 amp fuse is designed to handle a maximum of 10 amps.

A faulty circuit breaker or an open relay will have the same effect as a blown fuse. Circuit breakers are often used to protect circuits that may experience brief periods of overloading such as an A/C compressor clutch.

One way to check a circuit breaker is with a test light. Attach wire side of the test light to a known good ground and touch the metal tip of the test light to each side of the circuit breaker contact. If the test light glows when you touch each contact, the circuit breaker is good. If only one side glows, the circuit breaker is bad and you should replace it.