Principles of Operation

Trailer Lamps

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

The trailer lamps and trailer battery charge are supplied power by relays that are energized to correspond with the exterior lighting and ignition switch functions of the vehicle. The trailer tow relay coils are controlled by the output of the SJB.

If the vehicle is not equipped with the factory manufactured Trailer Brake Control (TBC) module, the vehicle supplies circuitry to support the installation of an aftermarket trailer electric brake controller (installed by the customer). To support the aftermarket trailer electric brake controller, the vehicle circuitry only supplies voltage, ground, stoplamp switch input and a brake controlling circuit to the trailer tow connector. The trailer electric brakes themselves are controlled by the aftermarket trailer brake controller and not the vehicle itself.

For diagnostics and a description of the factory manufactured TBC system, refer to Auxiliary Brake System Trailer Brake Control Module.