Table of contents: Detecting damage in a circuit ↓ Detection of poor grounding ↓
The protection of electrical circuits is provided by blade fuses, the color of which corresponds to the fuse protection current. The serviceability of the fuse is determined by the presence of a wire conductor connecting the fuse contacts. To replace a failed fuse, first turn off the corresponding electrical circuit, remove the fuse from the socket with tweezers. If the newly installed fuse immediately fails when voltage is applied, check the protected electrical circuit. If the fuse protects several circuits, they must be connected in turn in order to determine the faulty circuit by the blown fuse.
Detecting damage in a circuit
An 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 sources of electrical system malfunction, the vehicle electrical system diagrams are provided at the end of the 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.
Malfunctions 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 failed circuit before checking the rest of the components. Use the electrical schematics to determine which terminals need to be checked to locate the source of the problem.
A tester or voltmeter is used to find faults (lED tester); ohmmeter; 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.
Unreliable contact in the electrical circuit of any of the elements (usually due to poor connection or oxidation of contacts, or damaged insulation), you can perform a wire shake test. You need to shake the wire with your hand to check if the fault appears when the wire moves. This method can narrow down the range of possible. sources of fault to a particular wire.
Along with problems due to poor wiring connections, there are two main types of faults in an electrical system - open circuits and short circuits.
The circuit is opened as a result of a break or oxidation of a contact in the electrical equipment circuit, which will cause the electrical equipment element to switch off.
A short circuit in a section of a circuit causes current to leak from another circuit, usually directly to the body. A short circuit is 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. A short circuit usually causes the corresponding fuse to blow.
To check for continuity, connect a circuit tester or the negative probe of a voltmeter to the negative battery terminal or a grounded element. Connect the other probe to a 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 (at the same time, do not forget that some electrical circuits are switched on only when the key in the ignition switch is turned to a certain position).
Turn the switch 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 voltage is present (what do the voltmeter readings indicate), this means that the section of the circuit between the corresponding connection and the switch has no breaks.
Continue testing the circuit in the same manner. Finding a section where there is no voltage indicates that the open circuit has occurred between that point and the point of the previous test where there was voltage. Most open circuit problems are caused by a broken or loose connector.
To locate the source of the short circuit, first disconnect the load elements of the circuit (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 in its place. 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, this means that the circuit is shorted. If there is no voltage during testing, but the fuse still blows when the circuit load is connected, this indicates that the load element has failed.
Detection of poor grounding
The negative terminal of the battery is connected to the "ground" - the metal of the body, engine or gearbox. This means that the fastening of the electrical component and the body are part of the electrical circuit. An unreliable or oxidized fastening can lead to the failure of the component or disruption of its operation. In particular, the bulbs may burn with a dim light (especially if the grounding point of this light bulb is used to ground another piece of electrical equipment that is switched on), electric motors can run slowly, and the operation of one circuit can have subtle effects on the operation of another circuit. Remember that many vehicles use ground wires between certain components, such as the engine/transmission and the body, 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 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; otherwise, check the connection as follows.
If there is no ground, disassemble the connection and clean the body area and the wire terminal (or the element's 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, apply a layer of Vaseline or silicone grease to prevent future corrosion.