The composition of the electrical circuits of the car includes a consumer, switches, relays and wires connected according to the attached diagram (see below). Before you start troubleshooting, you should study the diagram and determine the possible source of the malfunction. For example, the task of troubleshooting is greatly facilitated if it is possible to check the health of other consumers directly or indirectly connected to the suspected circuit.
If there is a failure of several consumers, then the most likely cause is a broken ground connection or a blown fuse. As a rule, failures of electrical equipment are caused by weakening of contacts or their corrosion, blown fuse or jumper melting. Troubleshooting is usually done with a tester (voltmeter) or a test lamp, which are connected between the section of the faulty circuit and a well-stripped ground.
By connecting a tester or a lamp in series along the circuit loop, you can identify a faulty section, which is detected by a power failure or lamp extinction.
To search for a short circuit in the wires, you should get the fuse of the circuit under test and connect a lamp or a voltmeter to the gap. A short circuit with ground is indicated by the lamp lighting up when the wires are wiggled from side to side (the tester should show the voltage). When checking, it should be borne in mind that some consumers receive power when the ignition key is in the ACC or Run position.
To check the reliability of the connection to ground, connect through an ohmmeter (or through a test lamp with a battery) a checked wire-to-ground connection and a well-cleaned ground area. If the ohmmeter shows a circuit (or the lamp will turn on), then the ground connection is reliable. Otherwise, ground contact is broken. Keep in mind that in most cases, the ground serves as a return conductor connecting the circuit to the negative pole of the battery. Therefore, a broken ground connection, or an open circuit in the return current to the battery, can be the main cause of failure.