The defective fuse is replaced and after switching on the power consumer it is necessary to check whether the fuse does not immediately burn out again. If the fuse burns out again, the fault must be found and eliminated - as a rule, it is a short circuit. This means that somewhere, perhaps also inside the device, the ground and the positive conductor are connected to each other.
The second step of checking: if the incandescent lamp does not light or the electric motor does not work with a good fuse, it is necessary to check for the presence of supply voltage.
Testing a 12 volt incandescent lamp
Remove the bulb and inspect it. If the bulb is burnt out or loose in the socket, it should be replaced.
To eliminate doubts about the lamp's serviceability, proceed as follows: connect one conductor to the positive (+) and the other to the negative (-) pole of the battery, and connect the free ends of the conductors to the lamp. If the lamp does not light, it should be replaced.
Note: If necessary, clean rusted or bent lamp and socket contacts and restore them to a perfect condition.
If the lamp is in good condition, insert the lamp and turn it on. If the lamp does not light, check for supply voltage. To do this, connect one electrode of the control lamp to a reliable ground of the engine (clean metal surface) or directly with the negative pole of the battery. The other electrode of the test lamp (+) must either be connected to the current-supplying plug or inserted into the current-supplying wire.
If the control lamp now lights up, but the incandescent lamp still does not light up, then there is a break in the ground wire. To check this, install a jumper from the ground to the lamp socket. The lamp should light up.
If the lamp's current-carrying conductor has no voltage, i.e. the control lamp does not light, it is very likely that the switch is faulty. Checking the switch is described in the next chapter.
Checking Electric Motors
In order to increase comfort, more and more small electric motors are used in the car. These are electric motors of window lifts, sliding roof panels or central locking systems. Each electric motor is switched on when necessary via a switch, in most cases manually.
Check the fuse for the corresponding electric motor and replace the fuse if necessary.
Note: the electric motors of the electric windows and sliding roof panel are equipped with protection machines that, in the event of an overload, turn off the voltage supply to the electric motor and turn it on again after a while. Before turning the electric drive on again, it is necessary to eliminate the cause of the electric motor overload. The overload can be caused by icing of the window panes or contamination of the window lifter guide rails.
If the fuse blows again immediately, a short circuit has occurred.
To definitely determine whether the electric motor is working properly, it is necessary to connect it directly to the car battery with two auxiliary wires with a diameter of approximately 2 mm. The positive pole of the battery must be connected to the positive connector of the electric motor, and the negative pole to the negative connector. In doubtful cases, the location of the positive and negative connectors of the electric motor is determined in accordance with the electrical diagram. If necessary, the electric motor is removed. All electric motors of the car are supplied with an on-board voltage of 12 to 14 volts. If the electric motor now works normally, the cause of the malfunction was the lack of supply voltage.
Note: If the motor rotor rotates slowly or intermittently, the cause may be worn carbon brushes, which should be replaced.
If the electric motor is running, use the electrical 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 with a test lamp. Since a large current flows through the electric motor, you can use a regular incandescent lamp as a test lamp. It is equipped with sharp electrodes that can be used to pierce the connecting wire. This allows you to easily determine the presence of supply voltage.
If voltage is not supplied to the electric motor, the supply circuit is faulty. In accordance with the electrical circuit, find the fault in the wiring and fix it. Electric motors, due to the need for high currents, usually have an additional switching relay.
If no fault was found, check the switch.
If there is a defect in the wire, it is quite difficult to localize the defect, so it is advisable to lay a new wire.
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