Try, try again. If you are lucky, it won't take you too long to get it back on in the right spot.

 

MULTIFUNCTION SWITCH, thats where i would start, GM does not know how to make a good working switch for there life of emm. If your wipers continue to work after you shut the switch off, why would it be soldier points in the wiper engine? Get a multifunction switch and see what happens i bet it will work perfect

 

Park position is controlled by the wiper pulse board, not by the multifunction switch. If the board gets messed up and does not see the shut down signal from the incoming wires, it can definitely stay running.

I have repaired more wiper motors than I care to remember for many different symptoms including not stopping when required.