Any switch can go bad. More likely, a loose wire is crossed and bypassing the switch. Can you feel those wires back there? I would check the wires where they go to the switch.
Even if there is a fuse for the fog lights, a bad fuse would give you no lights, not constantly on lights.
Suggest you contact Thor and ask for a schematic of the wiring. Ask for one of the plumbing, too, while you are at it.
Only some of us learn by other people's mistakes, the rest have to be the other people!