Checking lamp switches and electric motors
Remove the switch.
For switches with multiple terminals, refer to the electrical diagram to determine which terminal should have voltage.
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 supply wire. Check the voltage supply according to the electrical diagram and install a new wire if necessary.
Checking the sensors-switches (alarms)
Sensor switches include, for example, oil pressure sensors and coolant or brake fluid level sensors.
Connect a probe or ohmmeter to the sensor terminals, removing the wires from them. For sensors mounted on the engine block, the sensor body serves as the ground pole.
When the switch is closed, the device should show a short circuit. When the switch is closed, the ohmmeter should show 0 Ohm, when open - infinity.
It is more convenient to check the serviceability of the coolant and brake fluid level switches by removing the wire from the switch with the ignition on and connecting it to ground, for example, on the engine block. The lighting of the control lamp on the dashboard indicates a switch malfunction.
When the engine is not running, the oil pressure sensor contact is closed (the control lamp is on), the switch opens only at a certain pressure.