The defective fuse is replaced, and after switching on the consumer of electricity, it is necessary to check whether the fuse immediately blows again. If the fuse blows again, find and fix the problem - usually a short circuit. This means that in some place, perhaps also inside the device, the mass and the positive conductor are connected to each other.
The second step of the test: if, with a good fuse, the incandescent lamp does not light or the electric motor does not work, it is necessary to check the presence of supply voltage.
Checking a 12 volt incandescent lamp
Remove the lamp and inspect. If the incandescent bulb is burnt out or weakly seated in the socket, it should be replaced.
To eliminate doubts about the health of the lamp, proceed as follows: connect one conductor to the positive (+), and the other to the negative (-) battery poles, and the free ends of the conductors are connected to the lamp. If the lamp does not light up, it should be replaced.
Note: If necessary, clean rusted or bent lamp and socket contacts and bring them back to perfect condition.
If the lamp is working, insert the lamp and turn it on. If the lamp does not light up, check for the presence of supply voltage. To do this, one electrode of the control lamp must be connected to a reliable engine ground (clean metal surface) or directly with the negative pole of the battery. Other indicator lamp electrode (+) must either be connected to a current-carrying plug, or plugged into a current-carrying wire.
If now the control lamp lights up, and the incandescent lamp still does not burn, then there is a break in the ground wire. To check this, install a jumper wire from ground to the lamp socket. In this case, the lamp should light up.
If the current-carrying conductor of the lamp has no voltage, that is, the control lamp does not light up, it is very likely that the switch is faulty. Checking the switch is described in the next chapter.
Checking electric motors
More and more small-sized electric motors are used in the car to increase comfort. These are the electric motors for the power windows, the sliding roof panel or the central locking system. Each electric motor, if necessary, is turned on through a switch, in most cases by hand.
Check the fuse of the relevant electric motor, replace the fuse if necessary.
Note: The electric motors for the power windows and the sliding roof panel are equipped with circuit breakers that, in the event of an overload, turn off the voltage supply to the electric motor, and then turn it on again after a while. Before restarting the drive, the cause of the motor overload must be removed. Overloading can be caused by icing on the windows or dirty window guide rails.
If the fuse blows again immediately, there is a short circuit.
To unambiguously find out if the electric motor is working, it is necessary to connect it with two auxiliary wires with a diameter of approximately 2 mm directly to the car battery. The positive pole of the battery must be connected to the positive motor connector and the negative pole to the negative connector. The location of the positive and negative motor connectors, in case of doubt, is determined in accordance with the electrical diagram. If necessary, the motor is removed. All electric motors of the car are powered by on-board voltage from 12 to 14 volts. If the motor is now running normally, the cause of the problem was a lack of supply voltage.
Note: If the motor rotor rotates slowly or intermittently, worn carbon brushes may be the cause and should be replaced.
If the electric motor is running, use the wiring diagram to determine which conductor supplies voltage to it when the switch is pressed and before the ignition is turned on.
Check the wire supplying voltage to the electric motor using a test lamp. Since a large current flows through the electric motor, you can use a conventional incandescent lamp as a test lamp. It is equipped with sharp electrodes that can be used to pierce the connecting wire. This allows a simple way to determine the presence of the supply voltage.
If voltage is not supplied to the electric motor, the supply circuit is faulty. Find the fault in the wiring according to the wiring diagram and fix it. Due to the need for high currents, electric motors usually have an additional switching relay.
If no fault was found, check the switch.
If there is a defect in the wire, then it is rather difficult to localize its defect, so it is advisable to lay a new wire.
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