1969 Wiper switch & electrical question

The switch doesn't need to be grounded to work. All it does is make or break the B+ connections to the wiper motor. It does nothing to the ground circuit. The extra connection is possibly the connection for electric windshield washers. Your car may not have that option but the switch is universal so it allways has the connection. Sounds like your problem may be a bad wiper motor or the switch has burned up internally.