Forgive the slightly off-topic question, but is this harness still available anywhere? For that matter, is there a plug-in harness still available for the rear end for the 7-way plug itself? Or is this a junkyard/hope-for-the-best find at this point?Did you use the pluggin harness? Then splice the wires onto the brake controller.
If you are using the factory 7 pin plug, and then using a adapter to convert it to 6 pin, I discovered something; They had two different wiring schemes for the 6 pin. The two different ways of wiring the 6 pin swap the aux 12v power with the brake power terminal.
So if you are using a adapter, look at it closely on the outside, it will usually be engraved if the brake is on the center pin or the aux power is on the center pin. You can take the adapter apart, and all the wires will be soldered except these two, which can be easily swapped with a small screwdriver. On my trailer I need the brake on the outside pins and the aux power on the center pin.
I have wired a regular 12v light bulb to the output of my brake controller, since I don't trust the LED in the controller(It sometimes lies to me for some reason). You may want to do the same, to verify if you really are sending voltage back there on the blue wire. If you are not, maybe you have a mechanical problem on the trailer?
All Tekonsha brake controllers have four wires out the back of them.
Black---Battery Pos.
White--Battery Neg.
Blue----Trailer Brakes
Red----Signal from brake switch
If your using the Ford OEM 4 connector harness, then the light Green wire connects to the Red wire on the controller. Every Ford truck with a towing package came with a 4 connector harness.
The after market 4 connector harness for Ford, the wire colors match the Tekonsha controller wires.
To The Warden; Those harnesses are available from most any RV store. I have the Ford harness for sale, PM me.