In the event of a failure of any node of the car, find the electrical circuit that includes this node, and sequentially trace through it the possible reasons for the failure of electric current to this node.
Very often, problems arise just because of the lack of contact in the wire connectors, caused by oxidation or unreliable connection of the latter, blown fuse, poor connection with «weight» due to oxidation of the connecting wires, failure of the relay.
Therefore, before checking and replacing components and parts of electrical equipment, carefully check the circuit and eliminate the listed causes of failure.
Most checks are performed with a tester or voltmeter. You can also use a 12 volt test light with two wires. Before troubleshooting, carefully study the wiring diagram to get an idea of where the device or test lamp should be connected to which points in the circuit.
Sometimes, in order to localize the failure of electrical equipment, it is enough to move the wiring by hand and use the device to determine the appearance of voltage in the problematic section of the circuit. In addition to poor contact in electrical connections, wire breaks or short circuits often become causes of failure, i.e. connection with «weight».
In the event of an open circuit, the electrical current is interrupted, but this does not cause the fuse to blow.
In case of a short circuit, which occurs due to damage to the insulation of the wires (aging, wire pinching at the points of contact with the body), the electric current becomes very large, which leads to blown fuse protecting the corresponding section of the circuit.
To detect an open circuit, do the following:
- Connect the test lead or negative voltmeter lead to the negative battery terminal. To do this, you can use a reliable contact with the body (not covered with paint);
- connect the other output of the device to the contact connector in the circuit under test, preferably closest to the positive terminal of the battery or fuse;
- apply voltage to the circuit under test (note that some circuits are only powered when the key is in a certain position in the ignition) and by the presence or absence of voltage on the device, make sure that the circuit under test is in good condition or open;
- continue checking the circuit according to the same method until you find the place of the break;
- repair the chain defect, the main cause is corrosion of the joints or poor contact in them.
To detect a short circuit in a circuit, do the following:
- disconnect, having determined from the wiring diagram, current consumers - lamps, heating elements, electric motors, etc.;
- remove the appropriate fuse from the unit and connect the instrument wires to the contacts of the fuse socket;
- apply voltage to the circuit under test (note that some circuits are only powered when the key is in a certain position in the ignition) and visually determine the presence or absence of an indication on the device;
- the presence of a reading on the device indicates a short circuit in the circuit, the absence of a reading means a malfunction in the composition of electric current consumers.
The electrical equipment of the car is made according to a single-wire circuit, i.e. negative conclusions of the absolute majority of electricity consumers are connected with «weight», which acts as a second wire. The engine block and gearbox are connected to «weight» bodies with braided copper bars, which are bolted. Very often in these compounds there are centers of corrosion, caused primarily by exposure to reagents for treating streets in the winter season. Corrosion degrades the electrical conductivity of circuits, which, in addition to outright failure in operation, often leads to a decrease in rotational speed
shafts of electric motors, for example, a windshield wiper or a heater fan. Corrosion in the connections explains the dim glow of the lamps and the influence of one electrical circuit on the operation of another.
To check the reliability of contact with «weight» specific consumer, disconnect the wires from the battery, then connect the tester in ohmmeter mode to the body and the consumer being tested. If there is a good contact, the ohmmeter should show zero.
Otherwise, disassemble the connection of the unit being checked, clean the contact point on the body and the contact surface of the consumer housing to bare metal (or lugs connecting to «weight» wires). Assemble the joint by carefully tightening the fasteners. Lubricate the outside of the joint with petroleum jelly or silicone grease to prevent corrosion.