I was wondering if anyone here had any knowledge of factory brake controller wiring. I have a 1990 F250 with a nice factory harness that was never hooked to a controller. It has enough wires for a 7 pin connector in the rear as well as a reversing horn. My problem is that the factory harness in the cab for the controller has 3 wires. There is a RED power wire from the positive battery terminal, there's a BLUE wire that goes to the back for the power brakes, and there is Red-green stripe wire that apparently goes directly to the back to power the trailer brake lights.
I know the standard blue/white/red/black of your average controller but what kind of controller has now or ever did have an output for the dedicated trailer brake lights? If there never was one, what was the purpose of that Red-green stripe wire? Why couldn't they tap into the brake light wires in the rear? What was Ford's logic?
The Red-green stripe wire doesn't tie into anything else.
Thanks for your help.
-mike

 

Just for clarity is the red-green always hot or is it only hot when you hit the brake pedal?

 

The Red-green stripe wire is not powered at all. It is a Ford factory wire that goes from the cab near where a controller would be and goes along the frame with the other towing harness wires to the back and is labeled 'Trailer Brake Stop Lamps.' I even have the factory wiring blueprint. It ties in with nothing else which leads me to believe that it was connected to the brake pedal in some way or was an output from some old style brake controller. I can't find anyone who has a setup like this and I wanted to have a professional setup. It must connect to something up front or why else put it in? Someone must have come across this before.
cheers,
-mike

 

 

That looks similar to what I found in my '88 F250. I don't remember much about how it was wired though. If I didn't use the wire running to the back of the truck, I clipped it in the engine bay and used it just to pass through the firewall without having to make a new hole.

I think one of the wires was connected to a transformer attached to the frame rail under the the bed. I haven't a clue what the hell it was supposed to be for and ripped it out as the connections had corroded anyways.

Perhaps it was supposed to be used with some ancient brake controller that would control the trailer lights as well as the brakes instead of pulling the power from the regular brake lights (which is actually a smart idea, but really bad if the controller craps out and you lose lights and brakes).

I would use the blue wire to connect to the trailer brakes, the red for power, and splice in a line from the brake pedal switch to trigger the brakes, then attach a ground somewhere under the dash. Make sure the line from the battery has a fuse or circuit breaker installed.

 

I may do that. It does seem odd to have such a nonstandard wiring system. I am surprised that there is so little info on a factory product in the days of the internet.