A typical electrical circuit consists of an electrical component (pump, light, motors, fan, etc.), any switches, relays, fuses, fusible links or circuit breakers related to that component, and the wiring and connectors which link the component to both the battery and the chassis (which is connected back to the battery to complete the circuit).
If you have the wiring diagram, fault finding is simplified, as you can identify multiple components included in the particular circuit. The possible fault can be narrowed down by noting if other components related to the circuit are operating properly. If several components or circuits fail simultaneously, the problem is likely to be related to a shared power/fuse or earth connection.
Electrical problems usually stem from simple causes, such as loose or corroded connections, a faulty earth connection, a blown fuse, a melted fusible link, faulty sensor or a faulty relay. Before testing the components of the electrical circuit, visually inspect the condition of all fuses, wires and connections in a problem circuit.
The basic tools for fault finding in electrical circuit is a basic Digital Volt Meter (DVOM) which will enable you to check for volt, amperage, continuity and resistance and a test light (for voltage drop and load test) . For more advanced faultfinding a scope can be used.
To find the source of an intermittent wiring fault a wiggle test can be performed on the wiring. This involves wiggling the wiring by hand to see if the fault occurs. Using this technique the fault can be narrowed down to the source of the fault to a particular section of the wiring. Intermittent wiring faults usually occurs due to poor or dirty connections, or a damaged wiring insulation, or internally broken wiring inside the insulation where movement is present (such as wiring going to trunk).
Electrical problems usually boil down to three types of fault: