Before attempting to determine the source of a fault, study the relevant electrical circuit diagram to gain an understanding of the components in that circuit. The number of possible sources of failure can be reduced by checking the operation of other components in the circuit. If several components or circuits fail at the same time, the fuse common to these circuits or components may be faulty, or the connection to the body - the "ground" - may be broken.
The causes of the malfunction may be loose or oxidized connectors, poor contact with the body, blown fuses or faulty relays. Visually inspect the condition of all fuses, wires, and connectors in the faulty circuit before proceeding to check the remaining components. Use electrical schematics to identify the terminals that need to be tested to locate the source of the fault.
The basic tools needed to locate the source of the fault are a tester or voltmeter, a 12V test lamp, an ohmmeter, a battery and a set of wires with probes, a jumper, preferably with a circuit breaker or fuse, which is used to bypass the wires or components being tested.
In addition to poor wire connections, there are two other main types of faults that can occur in an electrical system: open circuits and short circuits.
As a result of a break, the circuit opens, the current is interrupted, causing the electrical equipment element to turn off.
To check the integrity of a circuit, connect a circuit tester or voltmeter: one lead to the negative terminal of the battery or a grounded element, and the other to a contact in the circuit being tested, preferably closest to the battery or fuse. The circuit being tested must be live from the battery unless the battery connector is not conducting or the fuse is blown (remember that some electrical circuits are only activated when the ignition key 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 component being tested.
If there is tension (what does the control lamp or voltmeter reading indicate?), this 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 the circuit is broken between this point and the point of the previous test where there was voltage. A break in the circuit is caused by damage or loosening of the connector.
To locate the source of the short circuit, follow these steps:.
Remove the appropriate fuse and connect the tester or voltmeter leads to the fuse terminals.
Turn on the power to the circuits, keeping in mind that some electrical circuits are only turned on when the key in the ignition switch is turned to a certain position.
If there is voltage in the circuit (what does the control lamp or voltmeter reading indicate?), this means that there was 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 the ground – the body, engine or gearbox. Lack of reliable contact or oxidation of the fastener may lead to failure of the element or disruption of its operation. Keep in mind that many vehicles use "ground" wires between certain components, such as the engine/transmission, and the body, in places where there is no direct metal-to-metal contact due to soft rubber mounts or paint.
To check the reliability of the element grounding, it is necessary to disconnect the battery and connect one of the ohmmeter leads to a reliably grounded element. Connect the other lead to the wire or connection to the body that needs to be tested. The resistance shown by the ohmmeter should be zero, otherwise check the connection as follows.
If there is any doubt about the reliability of the ground contact, disassemble the connection, remove any dirt and clean the contacts. When assembling, tighten the connector fastener; to prevent corrosion, apply a layer of technical petroleum jelly or silicone grease.