Thanks for the replies. No, it's not the brake light switch, but I suppose it could be some kind of kickdown switch. Perhaps I didn't describe the thing too well. It's posted to the "stopper" on the floorboard beneath the accelerator pedal. The switch would be activated when the pedal is floored. I followed the wiring, it's marked with VW labels. My car's a manual, but I guess the switch and wiring could still be there.