Table of contents: General description ↓ Finding a break in the circuit ↓
Note: Before starting work, refer to the precautions given in Chapter 1 this Section.
General description
1. An electrical circuit consists of electrical components, switches, relays, motors, fuses, reverse current relays, and wiring. To find the exact fault in an electrical circuit, the electrical connection diagrams are given at the end of this Section.
2. Before diagnosing an electrical circuit, first study the electrical wiring diagram. If several components fail at the same time, the problem may be related to a fuse or ground.
3. Electrical faults are usually caused by simple causes, such as corroded connections, defective grounding, blown fuses or defective relays (refer to Chapter 3). Visually inspect the condition of all fuses, wires, and connections in the application circuit before testing components. Use the electrical wiring diagrams to accurately locate the fault.
4. Basic tools required for troubleshooting electrical fault, circuit tester or voltmeter; stroboscope; ohmmeter; battery and a set of load resistors. Before troubleshooting the instrumentation, use the wiring diagram to determine where to make connections.
5. To locate the location of a break in the wiring, move the wiring. This method of investigation can be used in conjunction with other tests described in the following subchapters.
6. Besides broken connections, the two main types of electrical circuit failure are open circuits and short circuits.
7. Circuit damage caused by a break prevents current from flowing to the elements.
8. A short circuit is usually caused by a fault in the wiring insulation that allows the supply wire to touch either another wire or a grounded body component. The short circuit causes the fuse to blow.
Finding a break in the circuit
9. To detect an open circuit, connect one wire with a circuit tester or voltmeter to the negative terminal of the battery.
10. Connect the other wiring of the circuit being tested, preferably close to the battery or fuse.
11. Turn on the ignition.
12. If voltage is present, the circuit between the connector and the battery is good.
13. Continue checking the rest of the chain in the same way.
14. When a point is found where no voltage is present, the fault is between that point and the previous voltage tested point. Most faults can be caused by broken, corroded or loose connections.
Finding the location of a short circuit
15. Before you begin searching 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 ignition.
18. If voltage is present, there is a short circuit in the circuit.
19. If there is no voltage, this indicates internal damage to the electrical equipment.
Finding a short circuit to ground
20. The negative terminal of the battery is connected to the car body. This means that the engine, transmission and body form part of the circuit. Open or corroded elements can cause a range of short circuits in the electrical circuit, up to and including complete failure of the circuit.
21. Check if the component is properly grounded. Connect the battery connector and the wiring with an ohmmeter to a known good ground point. Connect the other wiring to the ground being tested. The ohmmeter reading should be zero; if not, check the connection as follows.
22. If the grounding is faulty, clean the components of the grounding contact surfaces to bare metal, and tighten the connectors securely when reassembling; if installing a wire clamp, use serrated spacers between the clamp and the body to ensure a clean and secure connection. Once the connection is made, lubricate it with Vaseline or other lubricant.
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