The switch is mainly used to close and open an electrical circuit. There are switches that open the connection to «weight» (-), as well as switches that break the connection with a positive potential (+).
Checking lamp and motor switches
1. Remove the appropriate switch. Simple switches have only two leads for connecting a wire. In this case, one output should always have (+), and on the other output, a plus appears after switching on. There are also switches with multiple terminals. For these switches, you should find out from the diagram which terminal should be energized. Turn on the ignition first, if necessary.
2. Check up tension by means of a control bulb. If the control lamp lights up, turn on the switch and check the voltage at its output terminal. If there is voltage, then it is safe to say that the switch is working. If there is no voltage at the input terminal, this indicates a break in the supply wire. It is necessary to check the power supply according to the electrical circuit, and, if necessary, lay a new wire.
Checking the sensors-switches
Sensors-switches are, for example, sensors for warning lights for the level of brake fluid, engine oil and coolant.
3. Attach a device to the two leads of the sensor to «ringing» (test light or ohmmeter). To do this, disconnect the wires from the sensor.
Attention! Sensors screwed into the cylinder block usually do not have a wire «masses» (-), so their attachment to «mass» (-) occurs through the cylinder block, on which the body of the sensor itself closes.
When closed (included) sensor, the device should show the passage of current. For such «ringing» it is best to use an ohmmeter: with a closed sensor, it should show 0 ohms, and with an open one - «oh om (infinite resistance).
The operability of switches such as coolant or brake fluid level sensors can be most quickly checked by disconnecting the power wire from it with the ignition on, which is then connected to «solid» «mass» (-), for example, to the cylinder block. If now the light on the instrument panel works, then the sensor is faulty.
A special case is the oil pressure sensor. When the engine is stopped, its contact is closed and when the ignition is on, the engine oil pressure warning light is on. And only when the engine is running, when a certain oil pressure is reached, the switch opens.