Trace the power feed until you find a point where it fails.
Use a multimeter or test bulb.
Get the wiring diagram to assist.
This will narrow down the area where the fault is.
It could be a relay/ wire/ bulb etc, depending what is in the circuit.
You can then test the relay.
If ok try a bypass wire.
Is the fog bulb ok?
Electrickery problems can be frustrating but just take your time and be methodical.
