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 battery charge are supplied power by relays that are energized to correspond with the exterior lighting functions of the vehicle. If equipped, the vehicle also supplies circuitry to support the installation of an aftermarket Trailer Brake Control (TBC) module (installed by the customer). The vehicle circuitry only supplies voltage, ground, stoplamp switch input and a controlling circuit to the trailer tow connector. The trailer electric brakes themselves are controlled by the aftermarket TBC module and not the vehicle itself.

Vehicles equipped with the heavy duty trailer tow package are also equipped with a trailer sway control feature. For diagnostics and other information regarding this feature, refer to Vehicle Dynamic Systems Testing and Inspection.