It could be several things, including wiring near the switch. However, the most common suspect is the relay. That relay is located behing the glovebox. Just remove the glovebox by taking out the half dozen or so screws that hold it in(use caution when replacing the screws that you do not over-tighten and break the plastic lip of the glovebox). The relay is behind it on the left side. As I recall, it is orange and rectangular (about 1x1x2, roughly speaking) and just plugs in. It would be good if you could borrow one you knew was working to see if that would cure your problem, as, since this is an electronic component, most place will not let your return it. But, if you plan to keep the car, just go ahead and buy one, as sooner or later, you'll need it.