Diag. Manual
"Parking Circuit: (Fig 12-28, 36)
Moving dash switch to OFF position opens both armature and shunt field circuits to ground at the dash switch. However, both of these circuits are still closed to ground through the parking switch.

Note: The shunt field circuit actually flows via dash switch back to wiper parking switch direct to ground which means that wiper is actually operating in LO speed during the parking cycle.

When the cam on wiper output gear opens the park switch contacts, the wiper is OFF and/or wiper crank arm should be in the park position."