I bought a new Prodigy P3 trailer brake controller for my 1997 F-250 Diesel. I found a plug under the dash....it was to the right of the 4x4 shifter under the dash/under the ash tray area. Now the new brake controller lights up and all, but displays "no trailer connected". I know it is not my trailer because i just had the trailer hooked to a newer truck and the electric brakes work fine. and I've tried the controller on this truck with 2 newer trailers. I looked on etrailer.com and they say that the plug for my trailer brake controller should be under the dash to the LEFT of my steering column. Do I have the wrong plug that just happens to fit the trailer brake controller? And also i bought the correct wire harness adapter for the new controller so i wouldn't have to do any splicing. All the trailer wiring is factory with no splices or cuts. I've tried groundin g the trailer to the truck with an extra wire also. Any ideas?

 

A previous owner wired the brake controller into my '97 F-250HD and apparently cut off the factory plug because everything is hard wired. But the wires disappear up behind the dash directly under the power port in the middle of the dash. That sounds pretty much like where you have your controller plugged in. Given that mine doesn't have the connector I can't be sure it's actually the factory harness in the original location, but it seems likely.

 

That's the right connector, all three of my trucks have it there, just a small 4 wire plug. I have discovered they wired some of the rear plugs differently from the factory. I hooked up to a car trailer with one for the first time and the running light circuit activated the trailer brakes.....It was all screwed up. are you sure the plug on the bumper is wired correctly?

Diesel Rod

 

I've had that same experience with the trailer brakes being on all the time. It was the adapter I used between the truck and the 6 way round trailer plug. You have to swap a wire inside the adapter. Some adapters are set up to charge batteries in a camper or whatever while youre driving and if its not set up correctly inside it will put the electric brakes on all the time on other trailers.