This illustration is typical of most wiper motor park switch adjustments. Although your Ford Shop Manual gets into an involved dissertation about how to properly adjust the park switch, it is a simple process. You want this switch open with the wiper motor at park. The adjustment screw moves the lower contact closer or further from the bridge (upper) contact. Clockwise adjustment moves the lower contact closer to the bridge. Counterclockwise moves it away from the bridge.
When the wiper motor is in operation, these contacts open and close as the gear reduction package rotates. Because the wiper switch is in the on position, contact to ground is maintained and the motor continues to run. When the wiper switch is turned off, we lose our primary ground, which leaves the park switch ground intact. The motor continues to run until the park switch ground is broken. Your goal is to have the contacts open when the wiper motor is in the parked position.