Checking lamp switches and electric motors
Remove the switch.
For switches with multiple terminals, refer to the wiring diagram for which terminal should be energized.
Check the voltage supply to the switch with a tester. If the lamp lights up, turn on the switch and check for voltage at the output terminal. If there is voltage, the switch is working.
The absence of voltage at the input terminal indicates a break in the current lead. Check the voltage supply according to the wiring diagram and lay a new wire if necessary.
Checking the sensors-switches (signaling devices)
Switch sensors include, for example, oil pressure sensors and coolant or brake fluid level sensors.
Connect a probe or ohmmeter to the sensor terminals by removing the wires from them. For sensors mounted on the motor unit, the sensor housing serves as a ground pole.
When the switch is closed, the instrument should indicate a short circuit. With the switch closed, the ohmmeter should show 0 ohms, with the switch open, infinity.
It is more convenient to check the serviceability of the coolant and brake fluid level sensors by removing the wire from the switch with the ignition on and connecting it to ground, for example, on the engine block. The burning of the control lamp on the dashboard indicates a malfunction of the switch.
When the engine is not running, the contact of the oil pressure sensor is closed (control lamp on), the switch opens only at a certain pressure.