Note: Before starting work, read the warnings given in section "Safety first!" and in section 1 of this chapter. The procedures in this chapter apply only to the main electrical circuits and should not be used to test electronic circuits, especially those related to the electronic control unit.
Basic information
1. A typical electrical circuit consists of electrical components: switches, relays, motors, fuses or circuit breakers, electrical wiring, and connectors that connect the components to each other and to the battery and chassis. To assist in troubleshooting electrical circuits, wiring diagrams are provided at the end of this manual.
2. Before troubleshooting an electrical circuit, first study the relevant wiring diagram and get a complete understanding of the components included in this circuit. The search for possible sources of malfunction is easier if you make sure that other components included in this circuit are working. If multiple components or circuits fail at the same time, the problem is likely with the fuse or ground wire.
3. Faults in electrical circuits usually stem from simple causes such as bad connectors, poor grounding, a blown fuse, or a faulty relay. Before you begin checking circuit details, inspect the condition of all fuses, wires, and connectors in the faulty circuit. Use the wiring diagrams to determine the order in which to test the circuit.
4. Basic tools for troubleshooting electrical circuits include a tester or voltmeter (a 12 volt test light may also be used for some tests); ohmmeter (to check the circuit for open wires); battery; a jumper, preferably with a fuse, which can be used to bypass the wires or electrical components being tested. Before working with the instruments, study the wiring diagram to determine the points where any measurements should be made.
5. To find the source "unstable" wiring faults (usually due to a bad connection, or damaged wiring insulation), you can just move the wires. If, when the wires move, the contact in the circuit either disappears or occurs, then the source of the malfunction is located in this place of the wiring. This verification method can be used in conjunction with any of the others described in the following subsections.
6. In addition to poor contact, there are two more main types of malfunction: open circuit and short circuit.
7. When the circuit is broken, the component is disconnected from the power source or from the ground. Either way, it won't work.
8. Circuit short circuits are usually caused by wiring insulation failure that allows the wire to touch either another wire or the housing. A short circuit usually destroys the fuse in the corresponding circuit.
Open Circuit Detection
9. To test for an open circuit, connect one tester lead or negative voltmeter lead to the negative battery terminal or a good ground.
10. Connect the second terminal of the tester to the connector on the circuit under test, preferably the one closest to the battery or fuse. At this point, battery voltage should be present if the wire itself from the battery or fuse is intact (be aware that some circuits are closed when the ignition switch is in a certain position).
11. Turn on the circuit, then connect the tester terminal at the location closest to the area under test.
12. If voltage is present (or indicator light is on), this means that the circuit section between the corresponding connector and the switch is good.
13. Continue checking the circuit in the same way.
14. When a point is found where no voltage is present, the fault will be between that point and the previously tested point. Check this section of the circuit for a fault.
Circuit short detection
15. Before checking the circuit for a short circuit, first disconnect the load from the circuit (load - components that consume power, types of light bulbs, motors, heating elements, etc).
16. Remove the appropriate circuit fuse and connect the tester or voltmeter terminals to the fuse terminals.
17. Turn on the circuit, bearing in mind that some circuits are closed when the ignition switch is in a certain position.
18. If voltage is present (or indicator light is on), it means that there is a short circuit in the circuit.
19. If no voltage is present during this test, but the fuse blows when the load is connected, this indicates an internal fault in the load.
Ground Fault Detection
20. The negative battery terminal is connected to "grounding"-block engine-gearbox-body. Only the positive wire is suitable for most consumers of electricity, and the metal of the body is negative. This means that the body mass is part of the chain. In this regard, loose connections can cause partial or complete breakage of the chain. In particular, lighting fixtures may dimly burn (especially if another circuit is switched on using the same ground point), engines (such as wiper motors or cooling fan motor) may rotate slowly and the action of one circuit may affect the operation of another. Please note that many vehicles use flexible ground straps that connect to the bodywork with components that do not have direct metal contact with it, such as an engine-transmission unit mounted on rubber pads
21. To check if the component is well grounded, disconnect the battery and connect one ohmmeter lead to a good grounding point. Connect the second wire of the ohmmeter to the component to be tested. The ohmmeter should show zero resistance; if not, check the ground connection as follows.
22. If there is a suspicion that the connection to ground is broken, disassemble this connection, clean both the contact point on the body and the wire terminal (or mounting surface of the assembly housing) to metal. Remove all traces of dirt and corrosion, and scrape off the paint with a knife so that a clean metal-to-metal connection is provided. Assemble the connection and carefully tighten the fasteners; if there are terminals at the ends of the wires, install serrated washers between the terminal and the housing to ensure a secure connection. Lubricate the outside of the joint with petroleum jelly or silicone grease to prevent corrosion.