Usually the main task of the switch is to close and open the current supply circuit. There are switches that open the connection to «weight» and switches that open the positive voltage supply circuit.
Checking lamp and motor switches
Remove the corresponding switch.
A simple switch has two wire contacts. In this case, voltage is supplied to one of the contacts constantly, and to the other - when the switch is actuated. There are also switches with multiple contacts. For such switches, you need to find out from the electrical circuit diagram which contacts are energized, if necessary, turning on the ignition.
Using a test lamp, check whether the switch is supplied with voltage. If the test lamp lights up, turn on the switch and check the output contact for voltage. If this is the case, then the switch is working properly.
If there is no voltage on the input pin, then there is an open in the voltage supply circuit. Check the voltage supply according to the electrical circuit diagram and, if necessary, lay a new wire.
Checking the sensors-switches
To the switches (control switches) include, for example, the following: oil pressure warning lamp switch, brake and coolant level warning lamp switches.
Connect an ohmmeter to the switch contacts, for which remove the wires from them.
Attention: The switch, which is screwed into the cylinder block, usually does not have a wire «masses», because in this capacity, the circuit breaker housing is connected to «weight» through the cylinder block.
With the switch closed, the ohmmeter should show 0 ohms, with the switch open, infinity.
The operation of the coolant and brake fluid level switches is checked very quickly. To do this, with the ignition on, remove the wire from the switch and attach it to a good ground. If the control lamp on the panel of devices lights up, the switch is faulty.
The oil pressure warning light switch works differently: when the engine is off, its contacts are closed (control lamp on), and when a certain oil pressure is reached, the switch opens.