The first step should always be to check the fuse if the electrical component being tested is protected by one. The assignment of the fuses is shown on the fuse box cover.
The defective fuse must be replaced and checked to see if the new one burns out immediately after the power consumer is turned on.
In this case, you must first find the cause of the malfunction. As a rule, the problem is a short circuit.
This means that in some place, sometimes in the electrical device itself, the points of mass (-) and positive potential (+) are short-circuited.
Step two: If the incandescent lamp does not light with a working fuse, or, for example, the electric motor does not rotate, then you need to check whether the power supply is being supplied.
Checking an incandescent lamp
1. Unscrew the bulb and inspect it. If the filament has burned out or the glass bulb is not seated tightly in the base, then the bulb must be replaced.
To make sure the lamp is working properly, proceed as follows: connect two wires directly to the battery terminals and attach them to the lamp. Polarity does not play any role. One of the wires goes to the current contact, and the other to the lamp socket.
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If the lamp still does not light, replace it. But in this case, you need to be sure that the contacts of the lamp and the socket are not covered with corrosion.
If necessary, sand corroded or bent clamps and terminals with abrasive paper to restore reliable contact.
2. Put the bulb back in place and turn it on if it is working properly. If the bulb does not light, use a test light to check the power supply.
To do this, connect the test lamp to the "ground" (-). This means that one of the test lamp contacts must be securely connected to the engine housing (pure metal) or directly to the negative terminal of the battery.
Touch the other contact (+) to the power plug or directly to the power cord.
If the test lamp now lights up, but the lamp being tested still does not light up, this means that the connection between the lamp and the "ground" (-) is broken. To check this, attach an auxiliary wire connected to the car body to the lamp socket. The lamp should now light up.
If there is no voltage on the power supply wire, i.e. the control lamp does not light, then it is very likely that the switch is faulty. In this case, it is necessary to "ring" the switch.
Checking Electric Motors
An increasing number of functions related to the comfort of the car are performed by small electric motors. They operate, for example, the window lifts, the sunroof or the central lock.
Each motor is switched on, if necessary, by means of a separate switch, usually manually.
3. Check the fuse of the corresponding electric motor. Replace if necessary.
Attention! The electric motors of the window lift and the sunroof have protection machines that switch off when overloaded and switch on again after a while. Before switching on again, you must eliminate the cause of the overload. This may be caused by ice on the glass or contamination of the window lift guides.
If the fuse immediately blows again, then this indicates a short circuit.
To determine whether the defect is related to a malfunction of the electric motor, connect it with auxiliary wires (with a cross section of 2 mm) directly to the battery or the corresponding battery terminals.
In this case, it is necessary to observe the polarity. In case of doubts about the correctness of the chosen polarity, it can be checked using the switching diagram. But in this case, you will have to remove the electric motor.
All electric motors of the car are powered by the on-board voltage (12-14 Volts).
If the motor operates normally after power is supplied through the auxiliary wires, it means that no power was supplied to it.
If the electric motor rotates too slowly or intermittently, then it is possible that the graphite (carbon) brushes are worn out. In this case, the electric motor brushes need to be replaced.
If the engine is running, then, using the electrical diagram, determine which wire supplies voltage to it when the ignition and switch are on.
4. Check the electric motor supply wire with a test lamp. Since electric motors consume a lot of current, you can use a regular test lamp. The connecting wires of this test device have sharp probes that can pierce the insulation of the wire, which makes it easy to check the voltage.
Attention! The windshield wiper motor has special terminal markings, see the relevant chapter.
If the voltage does not reach the electric motor, this indicates a power supply malfunction. It is necessary to find and eliminate the malfunction according to the circuit diagram.
Electric motors, due to their high current consumption, usually have an additional switching relay. The procedure for checking the relay is given in the corresponding chapter.
5. Check the switch if no fault is found.
If a wire is broken, it is more practical to lay a new one, since it can be difficult to locate the location of the wire break.