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Wiper/Washer Systems - Liftgate: Operation

The wiper can only be operated with the ignition switch in the run or accessory position. There are 4 terminals on the motor and gearbox assembly. Terminals 1 and 2 are for the park switch and 3 and 4 are for the motor. See  Fig 1 . 

Fig 1: General Motors Liftgate Wiper Motor Assembly
G09358871Courtesy of GENERAL MOTORS COMPANY

Turning the dash switch to "ON" position provides 12 volts to motor terminal 3. The circuit is completed to ground through motor terminal 4, thus operating the wiper motor. See  Fig 2 .  Turning the switch to the "OFF" position provides 12 volts to motor terminal 3 through the park switch. The wiper will continue to operate until a cam, located in the transmission housing, opens the park switch contacts. The cam opens the park switch contacts when the wiper blade reaches the correct park position. See  Fig 2 . 

Fig 2: General Motors Liftgate Wiper & Washer System Circuit Diagram
G09358872Courtesy of GENERAL MOTORS COMPANY

Pushing the wash button in completes the washer motor circuit to ground and turns the washer motor on, which operates the pump. The pump allows direct control of the amount of solution delivered to the back glass and shuts off as soon as the wash button is released. The wiper will continue to operate until the dash switch is returned to the "OFF" position.