Note. Before starting work, see the precautions given in Head of this Section. The following checks only apply to main electrical circuits and should not be used on ELECTRONIC circuits.
General description
1. The electrical circuit consists of electrical components, switches, relays, motors, fuses, reverse current relays, electrical wiring. To find exactly the fault in the electrical circuit, the wiring diagrams are given at the end of this Guides.
2. Before diagnosing an electrical circuit, first study the wiring diagram. If several elements fail at the same time, the problem may be with a fuse or ground.
3. Electrical faults are usually caused by simple causes such as corroded connections, faulty ground, blown fuse or defective relay (follow Chapter 11). Visually inspect the condition of all fuses, wires, and connections in the applied circuit before testing components. Use wiring diagrams to pinpoint the exact location of the problem.
4. Basic tools required for troubleshooting electrical faults: circuit tester or voltmeter, stroboscope. ohmmeter, battery and a set of load resistors. Before troubleshooting instrumentation, use the wiring diagram to determine where to connect to the circuit.
5. To find the source of an intermittent wiring fault (usually due to a loose connection, or damage to the insulation of the wiring), the method is applied «movements» wiring. In this way, it is possible to narrow down the fault area to a specific circuit. This verification method can be used in conjunction with any of the tests described in the following subchapters.
6. In addition to problems due to a loose connection, there can be two main types of faults in an electrical circuit: an open circuit or a short circuit.
7. As a result of an open circuit, the component powered by it stops working, but this is not related to the fuse.
8. As a result of closing the circuit, the current begins to flow along a different path, usually at «mass». A short circuit is usually caused by insulation failure causing the supply wire to touch either another wire or «grounded» component, such as a body. A short circuit will usually cause the related fuse to blow.
Finding an open circuit
9. To test the circuit for an open, connect one tester or voltmeter lead to the negative battery terminal or a good «mass».
10. Connect the other wire to the connector of the circuit under test, preferably close to the battery or fuse.
11. Turn on the circuit, remembering that some of them are only energized when the key in the ignition is turned to a certain position.
12. If voltage is present (indicated by a tester or voltmeter), this means that the part of the circuit between this connector and the battery is OK.
13. In the same way, continue to check the rest of the chain.
14. When a no-voltage point is found, the fault is between that point and the previous energized test point. Most failures can be caused by broken, corroded or loose connections.
Search for a short circuit
15. Before starting the search for a short circuit, disconnect the electrical equipment from the circuit.
16. Remove the appropriate fuse from the circuit and connect a tester or voltmeter to the fuse connection.
17. Turn on the circuit, remembering that some of them are only powered when the key in the ignition is turned to a certain position.
18. If voltage is present (indicated by a tester or voltmeter), this means that part of the circuit between this connector and the battery is shorted.
19. If there is no voltage, but the fuse still blows with the load connected, this indicates a fault in the load itself.
Short circuit detection «mass»
20. The negative battery terminal is connected to «earth» This means that the mount of the electrical component and the body form part of the circuit. Loose or oxidized fasteners can cause short circuits in the electrical circuit. In particular, the lights can dimly burn (especially when another circuit connected to the same point is on «masses»), electric motors spin slowly (e.g. wiper or radiator fan motors), and the operation of one circuit may affect the operation of another. Note that many vehicles use ground straps between some components, such as the engine/transmission block to the body where there is no contact «metal-metal» between components due to flexible rubber pads, etc.
21. To check if the component is securely connected to «weight», disconnect the negative cable from the battery and connect one ohmmeter lead to a good «mass». Connect the other wire to the tested ground contact. The resistance must be zero; if not, check the connection as follows.
22. If a defective ground contact is suspected, disassemble the connection and clean to bare metal the body and wire terminal or ground contact contact surface. Then securely tighten the fasteners of the connection; if a wire terminal is installed, use serrated washers between the terminal and the body to ensure a good electrical connection. To prevent future corrosion, coat the joint with Vaseline or silicone grease.