Contents: General description ↳ Detecting a broken chain ↳ Detecting the source of a short… ↳ Detecting poor grounding ↳
General description
A typical electrical circuit consists of an electrical component, switches, relays, fuse motors, circuit breakers, wires, and connectors that connect the electrical component to the battery and body. To help you find the source of a fault in your electrical system, there are vehicle electrical diagrams at the end of this manual.
Before attempting to determine the source of the fault, first study the relevant electrical diagram to obtain an understanding of the components installed in that circuit. The range of possible sources of the fault can be narrowed down by checking the operation of other components included in the circuit. If several components or circuits fail simultaneously, the problem is likely to be in the fuse common to these circuits or components, or in the contact with the body.
Electrical problems are usually caused by simple problems such as loose or corroded connectors, poor contact with the body, blown fuses, a melted fusible link, or a faulty relay. Visually inspect all fuses, wires, and connectors in the faulty circuit before checking the rest of the components. Use the wiring diagrams to determine which terminals need to be checked to locate the source of the problem.
The main tools needed to locate the source of the fault are a tester or voltmeter (a 12 volt light bulb and a pair of wires with probes on the ends, can also be used to perform some tests); ohmmeter; battery and a set of wires with probes, a captive piercing, preferably with a circuit breaker or fuse, which is used to bypass the wires or elements being tested.
To find the cause of unreliable operation of any of the elements (usually due to poor connection or dirty contacts, or damaged insulation), you can perform a test by shaking the wires. You need to shake the wire with your hand to check whether the fault appears when the wire moves. This method can narrow down the range of possible sources of fault to a particular wire.
Besides problems due to poor wiring connections, two main types of faults can occur in an electrical system - an open circuit or a short circuit.
Open circuit problems occur when there is a break in the electrical circuit that interrupts the flow of current. An open circuit will cause the electrical component to shut down.
Short circuit problems are caused by a short in a section of a circuit, which causes current to leak from another circuit, usually directly to the body. Short circuits are usually caused by a break in the insulation of the wires, allowing the wire to touch another wire or some grounded element, such as the body. Short circuits usually cause the associated fuse to blow.
Detecting a broken chain
To check for continuity, connect a circuit tester or the negative probe of a voltmeter to the negative battery terminal or a grounded component.
Connect the second probe to the connection in the circuit being tested, preferably the one closest to the battery or fuse. This section of the circuit should be live from the battery, unless the battery connector is dead or the fuse is blown (remember that some electrical circuits are only enabled 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 item being tested. If voltage is present (as indicated by the test light or voltmeter reading), the circuit section between the appropriate connection and the breaker is continuous. Continue testing the target in the same manner, and when you find a section where there is no voltage, the circuit is open between that point and the point where there was voltage previously tested. Most open circuit problems are caused by a broken or loose connector.
Detecting the source of a short circuit
To locate the source of the short circuit, first disconnect the load elements of the circuit (load elements of the circuit are elements that consume electric current, such as light bulbs, electric motors, heating elements, etc.).
Remove the appropriate fuse and connect the tester or voltmeter probes to the fuse terminals.
Turn on the power to the circuit, remembering that some electrical circuits are only turned on when the ignition key is turned to a certain position. If voltage is present (as indicated by the test light or voltmeter readings), this means that there is a short circuit in the circuit.
If there is no voltage when testing, but the fuse still blows when the circuit load is connected, this indicates that the load element has failed.
Detecting poor grounding
The negative terminal of the battery is connected to the "ground" - the metal of the body, engine or transmission, but many electrical components are connected in such a way that only the positive wire goes to them, and the current returns to the battery through the metal of the body. This means that the mount of the electrical component and the body are part of the electrical circuit. As a result, a poor or corroded mount can cause the component to fail or to operate erratically or poorly. In particular, light bulbs may glow dimly (especially if the ground point of the light bulb is used to ground another electrical component that is also on), electric motors may run slowly, and the operation of one circuit may have an imperceptible effect on the operation of another circuit. Remember that many vehicles use ground wires between certain components, such as the engine/transmission and the body, i.e. in places 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, it is necessary to disconnect the battery and connect one of the ohmmeter probes to a reliably grounded element. Connect the other probe 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 you suspect a lack of grounding, disassemble the connection and clean the body area and the wire terminal (or the element grounding surface) to bare metal. Carefully remove all traces of dirt, then use a knife to remove all paint so that reliable contact between the two metal surfaces is achieved. When reassembling, tighten the connector securely; when connecting the wire terminal, install a serrated washer between the terminal and the body surface to ensure a secure connection. When connecting, prevent future corrosion by applying a layer of Vaseline or silicone grease.
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