In my estimation, I'd say there is a 50-50 chance the light switch is the problem.

Everyone ALWAYS forgets that there are TWO sources of A+ for the fog lamps:
Light Switch
CLP/SSM (Central Locking pump - Security System Module)

Few "mechanics" will be any more effective at resolving this than you would be. I'd order the switch off eBay and see if it fixes it.



BUT FIRST......

Yank Fuses 25 and 26 from the under-hood fuse box. If the lights go out, the issue is in the CLP/SSM.

If you think the light switch is expensive, wait till you ask about the CLP/SSM.