Trailer Lamps
Overview
The trailer tow system consists of the following components:
- Trailer tow connector
- Trailer tow relays
- TBC module (if equipped)
- BCM
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 to shut down the circuit and set a DTC 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.
Vehicles with a class III hitch are equipped with circuitry to support an aftermarket TBC 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 Network Message Chart
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Headlamp switch status | FLM | Indicates the headlamp switch position to the BCM. When the BCM has turned the parking lamps on based on input from the FLM, voltage is also provided to the trailer tow parking lamp relay. |
| Turn signal switch_status | SCCM | Indicates the turn signal stalk position on the multifunction switch (left/right lane change or turn signal on or off) to the BCM. The BCM activates the left/right trailer tow stop/turn relays based on this input. |
| Selector lever (PRNDL) status | PCM | Indicates to the gear selector lever position to the BCM. When the selector lever is in REVERSE and the ignition in RUN, the BCM provides voltage to the trailer tow reversing lamp relay. |
Trailer Stop-Turn Lamps
The BJB supplies voltage at all times to the trailer tow stop/turn lamp relays. The BCM 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 also provides an overload protection of the trailer tow stop/turn relay coil output circuits. When an excessive current draw is detected, the BCM disables the affected trailer tow stop/turn relay coil circuit driver. REFER to REFER to Multifunction Electronic Modules .
Trailer Parking Lamps
The BJB supplies voltage at all times to the trailer tow parking lamp relay. The vehicle rear parking lamp output circuit from the BCM 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 supplies voltage at all times to the trailer tow reversing lamp relay. The vehicle reversing lamp output circuit from the BCM 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 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.
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 detects a low voltage concern, the BCM disables the RUN/START relay.