Checking switches for current flow

Most electrical consumers are turned on and off with a manually operated switch. In addition, there are switches with automatic drive. Such switches include, for example, a hydraulically actuated switch (brake pressure drop sensor) and a brake fluid level sensor.

In principle, a switch has the task of closing or breaking an electrical circuit. There are breakers that break the ground line and breakers that break the positive pole line.

Checking lamp and motor switches

Remove the appropriate switch.

Simple switches have only two leads for connecting a wire. In this case, voltage should be applied to one output (+), and after switching on / off - and to another output. Switches with multiple terminals are available. With these switches, the circuit diagram explains which terminal the voltage is to be applied to. If necessary, turn on the ignition beforehand.

Use a test light to check if voltage is being supplied to the switch. If the test lamp lights up, turn on the switch and check if the output terminal is also receiving voltage. If so. then the switch is found to be functioning.

If there is no voltage at the output terminal, it means that the power supply wire is broken. Check the voltage supply on the basis of the circuit diagram and, if necessary, lay a new wire.

Checking the switches-sensors

Switch-sensors, for example, are: a switch with a hydraulic drive, sensors for the level of brake and coolant.

Plug in the probe (control lamp / or ohmmeter) to the inlet and outlet wires of the switch, to do this, pull the wire off the switch.

Attention! Switches that are screwed into the engine block usually do not have a wire connecting them to the housing, as the switch housing. The top of the engine block serves as a grounding pole.

At the switched on switch, the probe should indicate "current flow". The best probe is an ohmmeter: when the switch is on, it shows zero ohms, and when it is off, it shows infinity.

The fastest way to roughly test the coolant and brake fluid level warning switches is by pulling the lead wire off the switch with the ignition on and pressing it to a well-grounded location, such as the engine block. If the warning light on the instrument panel comes on, the fault is in the switch. A special case is a hydraulically actuated switch (brake voltage drop sensor): when the engine is stopped, the contact is closed (warning light is on), the switch opens only at a certain oil pressure.