You can pull the switch and undo the tabs on the sides of the switch casing. This will allow you to open the switch and inspect the contacts, but be careful as there are 3 spring loaded contacts that will fall out, be sure not to lose those. Look for any burnt plastic or copper. If you don't find any, then try playing with the contacts for the fog light themselves. You'll see it if you pull on the knob as if you were turning the fogs on. There are two little arms that come off the center of the shaft, those are the fog light contacts. Try bending those down until they make a good connection with the copper base.
