Checking the switching relay
When an electrical consumer is turned on, the operating current flows to it through the relay. The easiest way to check the relay is to replace it with a known good one. But there is not always an extra relay, so the following method is suggested for the relay for switching on and fog lights.
Remove the relay from the socket.
Turn on the ignition and the corresponding switch.
Use a tester to check for voltage on the positive terminal. When the tester lamp lights up, it means voltage is present.
Otherwise, look for a break in the electrical circuit between the battery and the terminal.
Make a jumper from an insulated wire, strip the ends, connect the jumper on the relay block to the positive terminal of the battery with the output contact of the relay, which achieves the effect as if a replacement was made with a known good relay. The location of the terminals on the relay block is determined by the color of the wires or by the electrical diagram.
If the high beam headlights light up with the jumper, the relay is faulty.
If the high beam fails, check the headlights' connection to ground. Then use the electrical diagram to find and fix the wire break.
Install a new relay if necessary.