The easiest way to test the relay is to replace it with a known good one. This is usually done in a specialized workshop. Since the motorist in rare cases has the necessary new relay available. The following procedure is recommended for testing the switching relay, used, for example, to turn on the fog and headlights.
Remove the relay from the holder.
Turn on the ignition and the corresponding switch.
Check the voltage on the positive contact of the relay with the device. To do this, connect one wire of the device to ground, and carefully insert the other tip into the device. If the LED of the device lights up, then there is voltage. If the meter does not show voltage, check the circuit between the positive pole of the battery and the relay terminal.
Make a bridge out of insulated wire. Clean up its ends.
Connect the bridge in the relay holder to the terminal (+) with relay make contact output. This connection corresponds to the connections in a good relay. The location of the terminals in the relay holder can be found by color marking and by the diagram.
If after that, for example, the high beam lights up, then it can be argued that the relay is out of order.
If the high beam does not come on, find out if the headlight ground connection is OK. Find a broken wire using the wiring diagram and fix it.
If necessary, install a new relay.