Ever since I got it, my 1992 F250 has had a bad wiper motor. The symptom, which can be caused by several different kinds of faults, is that it didn't "park". That is to say, the switch turned the wiper motor on and off, regardless of setting. High speed always worked, but park never did. I proved that the motor was the problem by taking off the cover and cleaning the contacts, and having it work for a short time. Rather than fight corrosion and continually shave switch contacts, I decided to drop the forty bucks retail on a new window motor.