The main task of the switch is to close and open the electrical circuit. There are switches that open the ground wire and switches that open the positive voltage wires.
Checking lamp and motor switches
Remove the relevant switch.
Simple switches have only 2 wire connectors. In this case, the positive voltage (+) is always supplied to one socket, and after the switch is turned on, the positive voltage feeds the other socket. There are also switches with an increased number of connectors. According to the electrical diagram, you should find out which connectors in such switches should be energized, if necessary, first turn on the ignition.
Use a test lamp to check whether voltage is supplied to the supply connector of the switch. If the test lamp lights up, turn on the switch and check for voltage at its output connector. If there is voltage, it can be stated that the switch is working.
If there is no voltage at the power connector of the switch, then there is a break in the current supply circuit. Check the current supply circuit according to the wiring diagram and lay a new wire if necessary.
Checking the sensors-switches
Such switches include hydraulic switches for the lubrication system and sensors-switches for the level of coolant and brake fluid.
Connect a breaker tester (test lamp or ohmmeter) to the inlet and outlet wires of the switch, for which one wire should be removed from the switch.
Attention: Switches that are screwed into the engine block, as a rule, do not have a ground wire, since this function is performed by the switch housing.
When the circuit breaker is on, the tester should show the conductivity of the circuit breaker. This is best determined with an ohmmeter: when the switch is on, it should show 0 Ω, and when it is off, it should read ∞ Ω.
The operability of the sensor-switch of the coolant or brake fluid level indicator can be checked most quickly if, with the ignition on, remove the supply wire from the sensor and connect it to a reliable ground, for example, an engine block. If the indicator lights up, then the switch is faulty.
Distinctive feature of the hydraulic switch: when the engine is not running, the contact of the switch is closed (signaling device is on). Only at a certain pressure does the contact open and the signaling device goes out.