Relay test

Relays are installed in many electrical circuits. The switching relay works like a switch. Example: If the high beam is turned on with the manual switch, the relay is commanded to switch the current to high beam. Of course, it would be possible to supply current directly from the battery, by means of a light switch. But for all elements with high current consumption (high beam, wiper, fog lamp) a relay is connected to the circuit so as not to overload the switch, providing shorter current paths. Next to these combination relays are also functional relays, for example, for windshield wipers and washer systems or a warning buzzer for switched on exterior lighting.

Checking the switching relay

When the lighting element is turned on, the relay starts, i.e. using the switching current, the electromagnetic coil draws in the relay contact and thus closes the electrical circuit "operating current". The operating current through the relay goes further to the consumer. The easiest way to check the performance of the relay is to replace it with a working one. So sprinkled even in a car repair shop. Since the owner of the car rarely has a new relay immediately available, in such cases it is recommended to carry out the following operation in the case of so-called switching relays, which are used, among other things, to turn on the fog and headlights. The marking of the terminals shown here can also be shown differently, especially for serially installed relays.

Remove the relay from the holder.


Turn on the ignition and the corresponding switch.

First check with a voltage indicator whether voltage is applied to terminal 30 (+) into the relay holder. To do this, connect a voltage indicator to the case (-), and insert the other contact carefully into terminal 30. If the light emitting diode flashes, there is voltage. If the voltage indicator does not show voltage, then look for a break in the wire coming from the positive pole of the battery using the circuit diagram (+) to terminal 30.

Make a conductive jumper from a piece of insulated wire, stripping it to a shine.

Use this jumper in the relay carrier to connect terminal 30 (+) battery is always energized) with NO contact output on terminal 87. This work step is practically the same as when installing a good relay.

If with a jumper, for example, the main beam lights up, then we can assume that the relay is faulty.

If the high beam does not light up, find out if the connection to the housing at the headlights is in order. In this case, locate and repair the open in the line from terminal 87 to the main headlight using the wiring diagram.

Install a new relay if required.

Attention! If a defect in an electrical circuit that is equipped with one relay appears only periodically, then in this case, as a rule, the malfunction lies in the relay: the contact in the relay disappears or the contact sticks too much, while the rest of the time the relay functions normally. If a defect occurs, lightly tap on the relay housing. If the relay switches after this, replace it.