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.
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 or central locking.
Each motor is turned on, if necessary, with a separate switch, usually manually.
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 may be caused by frost on the windows or dirty window guides.
If the fuse blows again immediately, then this is a short circuit.
To establish unequivocally 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 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 circuit, determine which wire supplies voltage to it when the ignition is on and the switch is on.
4. Check up by means of a control bulb a feeding wire of the electric motor. Since electric motors consume a lot of current, you can use a conventional control 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 power failure. 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 testing the relay is given in the relevant 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.