Principles of Operation: Notes

WARNING: This page is about a different car, the 2012 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.

The trailer lamps and trailer battery charge are supplied power by relays that are energized to correspond with the exterior lighting and ignition state functions of the vehicle.

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 TBC module (installed by the customer). To support the aftermarket TBC module, 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 trailer brake control system, REFER to AUXILIARY BRAKE SYSTEM -- F-150 .

The trailer tow battery charge relay is controlled by the Body Control Module (BCM). If the BCM detects a low voltage concern when the ignition is in ACC or RUN, the BCM disables the trailer tow battery charge relay coil circuit.