Checking lamp switches and electric motors
Remove the corresponding switch.
Simple switches have only 2 wire connectors. In this case, positive voltage (+) is always supplied to one connector, and after the switch is turned on, positive voltage supplies the other connector. There are also switches with an increased number of connectors. According to the electrical diagram, you should find out to which connectors in such switches the voltage should be supplied.
Use a test lamp to check whether voltage is supplied to the switch power connector. If the test lamp lights up, turn on the switch and check whether voltage is supplied to its output connector. If voltage is present, the switch can be considered to be in good working order.
If there is no voltage at the switch power connector, then there is a break in the current-supply circuit. In accordance with the electrical diagram, check the current-supply circuit and, if necessary, lay a new wire.
Checking the sensor switches
Such sensors-switches include, for example, sensors-switches for brake fluid, engine oil and coolant levels.
Connect the device to test the switch (a test lamp or ohmmeter) to the supply and return wires of the switch, for which one wire must be removed from the switch.
Note: Switches that are screwed into the engine block usually do not have a ground wire, since this function is performed by the switch housing.
The best way to check this is with an ohmmeter: when the switch is on, it should show 0 Σ, and when it is off, it should show ∞ Σ.
Additionally, you should check the operation of the indicator lamp on the instrument panel: with the ignition on, remove the power wire from the switch and connect it to a reliable ground. The indicator lamp should light up.
[The information is posted on this resource: VWmanual]
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