Electrical System Fault Diagnosis - Searching for the Cause of a Short Circuit

First, disconnect the electrical load(s) of the circuit being tested (electrical loads, or the useful load of a circuit, are components whose operation consumes the current circulating in the circuit, such as lamps, electric motors, heating elements, etc.). Remove the fuse protecting the circuit under test and connect a test lamp or voltmeter to its fuse terminals. Apply power to the circuit. Remember that some circuits are powered only in certain ignition switch positions. If voltage is present at the fuse terminals, there is a short circuit in the circuit (wiggle the wiring harness, since a short circuit may be caused by chafed insulation and may be intermittent). If there is no voltage, but the fuse continues to blow after replacement when power is applied to the circuit, there is an internal fault in the electrical load(s), the switch, or the wiring insulation.