Analyze the Schematic

Look up the schematic for the problem circuit. Determine how the circuit should to work by tracing the current paths from the power source through the circuit components to ground (certain circuits contain a "How the Circuit Works" article). Also, trace circuits that share wiring with the problem circuit. The names of circuits that share the same fuse, ground, or switch, and so on, are referred to in each circuit schematic. Try to operate any shared circuits that you did not check in step 1. If the shared circuits work, the shared wiring is OK, and the cause must be in the wiring used only by the problem circuit. If several circuits fail at the same time, the fuse or ground is a likely cause.

Based on the symptoms and your understanding of the circuit's operation, identify one or more possible causes.