The first step should always be to check the fuse if the electrical assembly being tested is protected by it. The purpose of the fuses is given on the cover of the fuse box.
A defective fuse must be replaced and a new one checked to see if it blows immediately after switching on the electrical consumer. 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 are bridged (-) and positive potential (+).
Second step. If, with a good fuse, the incandescent lamp does not light, or, for example, the electric motor does not rotate, then you need to check whether the power is supplied.
Incandescent lamp test
1. Unscrew the lamp and inspect it. If the filament is burned out, or the glass bulb does not sit tightly in the base, then such a lamp must be replaced.
To make sure that the lamp is working, proceed as follows: connect two wires directly to the battery poles and attach them to the lamp. Polarity does not play any role in this. One of the wires goes to the current contact, and the other to the lamp socket. If the lamp still does not light up, replace it. But in this case, you need to be sure that the contacts of the lamp and the cartridge are not covered with corrosion. If necessary, treat corroded or bent clamps and terminals with abrasive paper and restore reliable contact.
2. Insert the light bulb into place and turn it on if it is working. If the lamp does not burn, then by means of a control bulb check up power supply. To do this, connect a test light to «mass» (-). This means that one of the test lamp contacts must be securely attached to the engine housing (pure metal) or directly to the negative battery terminal. Other contact (+) touch the power plug or the power cable directly. If now the control lamp lights up, but the lamp under test still does not light up, this means that the connection between the lamp and the «weight» (-). To check this, attach an auxiliary wire connected to the car body to the lamp socket. The lamp should now be on.
Attention! There are light bulbs that are directly connected by a housing on «mass» (-), for example, interior lighting bulbs.
If there is no voltage on the supply wire, that is, the control lamp does not light up, then it is very likely that the switch is faulty. In this case, it is necessary «ring out» switch.
Checking electric motors
An increasing number of functions related to ensuring the comfort of the car are performed by small electric motors. They actuate, for example, power windows, sunroof, central locking or aerial.
Each engine is turned on, if necessary, by a separate switch, but usually manually. The antenna drive is activated when the radio is turned on.
3. Check the fuse for the relevant motor. Replace if necessary.
Attention! The electric motors for the window and sunroof have circuit breakers that turn off when overloaded, and turn on again after a while. Before switching on again, the cause of the overload must be eliminated. This can be caused by frost on the windows, locks, or dirty window guides.
If the fuse blows again immediately, this indicates a short circuit.
To establish unequivocally whether the defect is due 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 appropriate leads from the battery. In this case, polarity must be observed.
In case of doubt about the correctness of the selected 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 on-board voltage (12-14 Volt). If the motor runs normally after applying power through the auxiliary wires, it means that it was not powered. If the motor rotates too slowly or intermittently, wear of the graphite (coal) brushes. In this case, the motor brushes must be replaced.
If the engine is running, then, guided by the electrical diagram, determine which wire supplies voltage to it, if the ignition is on and the switch is on.
4. Check up by means of a control bulb supplying to a wire of the engine. Since the motors consume a lot of current, you can use a conventional test light. The connecting wires of this tester have sharp probes that can pierce the wire insulation, making it easy to check the voltage.
Attention! The wiper motor has special terminal designations, see relevant chapter.
If voltage is not supplied to the motor, then this indicates a wiring problem. It is necessary to find and eliminate the malfunction according to the principle diagram. Due to the high current consumption, electric motors 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 the wire is broken, then it is more advisable to lay a new one, since it can be difficult to localize the place of the wire break.