2012 GMC Sierra Trailer Wiring | etrailer Call 800-298-8924 to get Expert Service ordering a Trailer Wiring for your 2012 GMC Sierra. Complete installation instructions and lifetime technical support on all Trailer Wiring purchases. Lowest price guarantee on accessories for your GMC Sierra and the fastest shipping available. 2012 GMC Sierra Hitch Wiring - CARiD GMC Sierra 2012, Trailer Hitch Electrical Connector Plug by Dorman®. 7 Way Terminals. 7 Way Terminals Connector. Restore the brake lights and turn signal on your trailer to proper operation with Dorman’s Trailer Hitch Plug. The Plug..