You say you have disconnected the lights. I am assuming that means you unplugged the socket from the lamps. Chances are that will tell you nothing. You already have a short at the lamps via the filament. Only the resistance keeps the fuse from blowing.

So, once the sockets are unplugged take a very close look at them and check for moisture or anything that could cause a short circuit. Even take the time to dry them out with a hair dryer just in case.

After that you will need to trouble shoot the wiring from the switch location to the sockets.

Others here more familiar with the intricacies of the xfire can chime in on how to remove the necessary panels and the right pin out on the switch.

I would also locate and download the service manual located here for free and study the wiring of the fog lamps to get familiar on what was on Karmann/MB/Uncle Walter's mind when they wired the car.

Good luck.

Tired