I Have a 1990 ford f150. The wipers only work on high, I put in a new switch and it didn‘t change. Then a day later I left home in a rain and they started working like they were supposed to. But about a 1/2 hour they quit working all but high and then they would slow down if the window started to get dry. Is this the motor or is there a relay somewhere?
try the relay first then if that don,t work then change the motor.
That trucks wiper motor usually grounds through it's case, so I do not think it is a bad ground. This sounds like a bad winding in the motor itself. Yea, change the wiper motor.
Pretty certain there is a rheostat for the wiper motor - that would explain still working on high. Sorry, don't know the location. Try tapping the motor and see if they restart. Old tech trick but accurate.
