2006 F 250 Trailer Wiring Diagram. The wires that run through the firewall are 'customer access' wires (firewall pass through) and aren't for the brake controller. Trailer wiring diagrams are available for most commercial trailers.
Trailer wiring diagrams are available for most commercial trailers. Specifically the harness that runs along the door. Not all trailers have reverse lights, so.
It does seem like a strange problem, but something similar happened to me when I wired my trailer a little loosely on the connectors.
Land Rovers are large SUVs intended for off-road use, making them a popular towing vehicle for outdoor enthusiasts.
A repair book for the make and model of your vehicle will have the diagram included in it. The wires that run through the firewall are 'customer access' wires (firewall pass through) and aren't for the brake controller. Here is the wiring diagram for the trailer wiring for your truck.