NICK-
Yep, there are three wires on most wipers and they will self park.
The way it traditionally works is this:
The motor is wired hot. That is, the + side of the circuit is always hot to one side of the motor armature brushes, and the parking circuit as well.
The motor is actuated by turning on the switch, which allows the other side of the armature brushes to ground out and run the motor (permanent magnet field motor type).
The park circuit consists of a cam, cam follower, and set of points. The points are wired to the hot wire on one side and to another ground wire (w/o a switch) on the other.
Turning off the switch still leaves the one side of the points hot, and they are grounded through the point set to the ground wire and keep the motor turning until the high spot on the cam opens the gap and the circuit is broken, stopping the motor rotation. This parks the motor and the blades.
The newer AFI (American Foreign Industries) motors may be somewhat different, I'm having trouble remembering exactly, and cannot find a direct answer on AFI's (Marinco's) website. I suggest you get your wiper motor model number and go to a West Marine or equivalent store and copy the installation directions out of a replacement motor box.
Did the factory, dealer, or ??? install your wipers?
Joe. :teeth :thup