I have a 71 Skylark that the wiper motor was inoperative. First I checked the different 12v power locations - fuse connection, 3 prongs on the motor. That was ok! It turns out the motor was not being grounded to the firewall. There is a brass ground strip that connects to one of the rubbers on the 3 legs. That strip had some corrsion on it and preventing the grounding. I took the strip out and cleaned it and where it connects to - case and the metal piece that goes through the rubber on the leg. Now the wiper motor works.
