Passenger side windshield wiper stopped working. What may be the cause? Driver side wiper works. Both were working then the passenger side just stopped moving. It moves easily by hand.

You will need to take the cowl off and replace all of the bushings. Most auto parts stores will have them in stock.

I have a 1987 dodge van, i had the same problem except both wipers stoped moving they were both lose and could be moved by hand,
the linkage had slipped off of the wiper motor arm due to a bad bushing.
the bushing is a hard plastic, or some simular material,i bought a new one in a package of assorted bushings at the parts store. the hardest part was getting the cowl off past the hood, and the wiper blade pivots,don't forget to grease the bushing with a suitable grease or you will hear a constant anoying squeek!
P.S i think the wipers on your truck should be simular if not exactly the same (i also have a1984 prospector)
Hope you get it fixed!