The motor has to be grounded, and so does the switch - the motor works by grounding the circuit through the switch to the lower instrument panel reinforcement. There's a stamped sheet metal ground plate shared by the headlight switch and the wiper switch, with a leg at the bottom that's screwed to the lower reinforcement, and a pigtail wire - if that plate or wire is broken, missing, or has the screw at the bottom missing, the wipers won't work. That plate is shown in the Assembly Manual in UPC 1, sheet B2, View "B", and in UPC 12, Sheet B2.