Take the switch out of the dash and take it apart. Chances are that the problem with the switch is that from the contacts arcing (which is normal), they aren't making good contact anymore. This happens alot on door switches for power windows and power door locks. I had the ones in my '88 bronco and my '88 F-150 out 100 times. Take the switch apart and GENTLY file the contacts down with light sandpaper or a fine nail file until all the black arc marks are gone. Good as new.