Trailer Lamps

Trailer Lamps

Overview

The trailer tow system consists of the following components:

- Trailer tow connector

- Trailer tow relays

- TBC (Trailer Brake Control) module (if equipped)

- BCM (Body Control Module)

Vehicles not equipped with trailer tow require a Ford authorized accessory kit to add this option. Adding bulbs/lighting to existing circuits can cause the BCM (Body Control Module) to shut down the circuit and set a DTC (Diagnostic Trouble Code) due to the unexpected current flow.

When the vehicle's rear stop/turn, parking lamps or reversing are illuminated, voltage is also supplied to a corresponding trailer tow relay located in the BJB (Battery Junction Box).

Vehicles with a class III hitch are equipped with circuitry to support an aftermarket TBC (Trailer Brake Control) module and provide voltage to the trailer tow connector when the ignition is in RUN for trailer battery charging.

System Operation

System Diagram





Network Message Chart

BCM (Body Control Module) Network Input Messages






Trailer Stop-Turn Lamps

The BJB (Battery Junction Box) supplies voltage at all times to the trailer tow stop/turn lamp relays. The BCM (Body Control Module) provides voltage to the trailer tow stop/turn lamp relay coils to correspond with the rear stop/turn lamp functions of the vehicle.

The BCM (Body Control Module) also provides an overload protection of the trailer tow stop/turn relay coil output circuits. When an excessive current draw is detected, the BCM (Body Control Module) disables the affected trailer tow stop/turn relay coil circuit driver. REFER to Field Effect Transistor (FET) Protection Description and Operation.

Trailer Parking Lamps

The BJB (Battery Junction Box) supplies voltage at all times to the trailer tow parking lamp relay. The vehicle rear parking lamp output circuit from the BCM (Body Control Module) is spliced to provide voltage to the trailer tow parking lamp relay coil to correspond with the parking lamp function of the vehicle.

Trailer Reversing Lamps

The BJB (Battery Junction Box) supplies voltage at all times to the trailer tow reversing lamp relay. The vehicle reversing lamp output circuit from the BCM (Body Control Module) is spliced to provide voltage to the trailer tow reversing lamp relay coil to correspond with the reversing lamp function of the vehicle.

Trailer Electric Brakes

If equipped with a class III trailer hitch, circuitry is provided to support the installation of an aftermarket TBC (Trailer Brake Control) module (installed by the customer). To support the aftermarket TBC (Trailer Brake Control) 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.

Trailer Battery Charging

The trailer tow battery charge relay is controlled by the output from the RUN/START relay. When the ignition is in ACCESSORY or RUN and the BCM (Body Control Module) detects a low voltage concern, the BCM (Body Control Module) disables the RUN/START relay.