69 Chevelle Wiper Motor will not turn off

[NEATSS]

I had the very same issue. The motor will not stop until it goes into park position. A coil holds the parking paw until until the switch is turned off. At that time the paw drops out and causes the blades to go to park which breaks contacts to stop the motor. The coil that holds the parking paw is not releasing, be it mechanical or electrical. With mine it seemed there was residual magnetism holding the paw and keeping it from activating. I could not find a mechanical cause. I replaced the coil assembly with a used one and problem solved.