Before attempting to determine the source of a fault, study the relevant circuit diagram to get an idea of the elements in this circuit. The number of possible sources of malfunction can be reduced by checking the operation of other elements included in this circuit. If several elements or circuits fail at the same time, the fuse common to these circuits or elements may be defective, or the connection to the body is broken - «weight».
Causes of a malfunction can be loose or oxidized connectors, poor contact with the body, blown fuses or faulty relays. Visually check the condition of all fuses, wires and connectors in the failed circuit before proceeding to check the rest of the elements. Use the wiring diagrams to determine the end clamps that need to be checked to find the source of the problem.
The main instruments needed to locate the source of a malfunction are a tester or voltmeter, a 12 V test lamp, an ohmmeter, a battery and a set of wires with probes, a captive puncture, preferably with a circuit breaker or fuse, which is used to bypass the tested wires or elements.
In addition to a violation of the reliability of wire connections, two more main types of malfunctions are possible in an electrical equipment system - an open circuit or a short circuit.
As a result of a break, the circuit opens, the current is interrupted, causing the electrical equipment to turn off.
To test continuity, connect a circuit tester or voltmeter, one lead to the negative battery terminal or ground, and the other to a terminal in the circuit under test, preferably one that is closest to the battery or fuse. The section of the circuit under test must be powered by the battery, unless the battery connector is not conducting current or the fuse is blown (do not forget that some electrical circuits are switched on only when the key in the ignition switch is turned to a certain position).
Turn on the circuit, connect the tester probe to the connection closest to the circuit breaker on the side of the element being tested.
If there is tension (as evidenced by a control lamp or voltmeter readings), which means that there are no breaks in the section of the circuit between the corresponding connection and the switch.
If a section is found where there is no voltage, then an open circuit occurred between this point and the point of the previous test, which had voltage. An open circuit is caused by a damaged or loose connector.
To locate the source of a short circuit, do the following.
Remove the appropriate fuse and connect the tester or voltmeter leads to the fuse contacts.
Turn on the power in the circuit, while not forgetting that some circuits of electrical equipment are turned on only when the key in the ignition switch is turned to a certain position.
If there is voltage in the circuit (as evidenced by a control lamp or voltmeter readings), means there is a short circuit in the circuit.
If there is no voltage during the test, and the fuse still blows when the same load is connected, then the load element has failed.
The negative terminal of the battery is connected to «mass» – to a body, the engine or a transmission. Lack of reliable contact or oxidation of the fastener can lead to failure of the element or disruption of its operation. Do not forget that many cars use «massive» wires between certain elements, such as the engine / transmission, and the body, that is, in places where there is no direct contact between metal elements due to the presence of soft rubber mounts or a layer of paint.
To check the reliability of the cell grounding, it is necessary to disconnect the battery and connect one of the ohmmeter leads to a reliably grounded cell. Connect the other lead to the wire or body connection to be tested. The resistance shown by the ohmmeter should be zero, otherwise check the connection as follows.
If the reliability of contact with «weight», disassemble the connection, remove dirt and clean the contacts. When assembling, tighten the connector fastening, apply a layer of technical vaseline or silicone grease to prevent corrosion.