Detecting damage in a circuit
A typical electrical circuit consists of an electrical component, switches, relays, motors, fuses, circuit breakers, wires, and connectors that connect the electrical component to the battery and the body. To help you find the source of a fault in the electrical system, the manual provides vehicle electrical diagrams.
Before attempting to determine the source of a fault, study the relevant electrical diagram to obtain an understanding of the components in that circuit. The number of possible sources of faults can be reduced by checking the operation of other components in the circuit. If several components or circuits fail simultaneously, the fuse common to those circuits or components may be faulty, or the connection to the body - "ground" - may be broken.
Causes of failure include loose or corroded connectors, poor contact with the body, blown fuses or faulty relays. Visually inspect the condition of all fuses, wires and connectors in the failed circuit before checking the rest of the components. Use the electrical diagrams to determine the terminals that need to be checked to find 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 elements being tested.
In addition to poor wiring connections, there are two other main types of faults that can occur in an electrical system: an open circuit or a short circuit.
The circuit is opened as a result of a break in the electrical equipment circuit, which interrupts the current, causing the electrical equipment element to switch off.
To check the continuity of a circuit, connect a circuit tester or voltmeter: one lead to the negative terminal of the battery or a grounded element, the other to a contact in the circuit being tested, preferably the one closest to the battery or fuse. The section of the circuit being tested should be energized by the battery, unless the battery connector is not conducting current 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, then connect the tester probe to the connection closest to the circuit breaker on the side of the component being tested.
If there is voltage (as indicated by the test lamp or voltmeter readings), then 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 there is a break in the circuit between this point and the point of the previous test where there was voltage. The break in the circuit is caused by a damaged or loose connector.
To detect the source of a short circuit (electricity consumers - lamps, electric motors, heating elements, etc.), remove the corresponding fuse and connect the tester or voltmeter leads to the fuse terminals.
Turn on the power to the circuits, remembering 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 (as indicated by the test lamp or voltmeter readings), then there is a short circuit in the circuit.
If there is no voltage when checking and the fuse still blows when the same load is connected, then the load element has failed.
The negative terminal of the battery connects to the ground - the body, engine or transmission. A poor or corroded connection can cause the component to fail or malfunction. Remember that many vehicles use ground wires between certain components, such as the engine/transmission, and the body, where there is no direct contact between metal components due to soft rubber mounts or a layer of paint.
To check the reliability of the element grounding, 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 checked. The resistance shown by the ohmmeter should be zero, if not, check the connection as follows. If there is any doubt about the reliability of the contact with the "ground", disassemble the connection, remove dirt and clean the contacts. When reassembling, tighten the connector mount, applying a layer of technical petroleum jelly or silicone grease to prevent corrosion.