Wiring question. 2004 F250 with tow mirrors but no harness at rear bumper?

[Tungsten]

I've got a 2004 F250 with extending tow mirrors and a hitch receiver. Not sure if the receiver is OEM or aftermarket. The previous owner had spliced in a 4-pole harness at the rear and did a crappy job of it. I'm redoing his work to set the truck up to tow a car hauler.

Gear to be used consists of:

• 8ga battery power feed fused and pulled from engine bay to rear bumper area by previous owner. Checks out fine.

• Tekonsha Prodigy P3 brake controller that I purchased.

• Tekonsha to Ford OEM controller wiring harness.

• 7-pole and 4-pole (dual) connection receptacle for the truck-side of the trailer wiring.

I've located the harness plug-in point under the dash. I assume that I may have to add the proper fuse to the power distribution block under the hood to get power to the OEM harness plug. Not a problem.

I picked up a spool of blue 12ga wire just in case I need to pull my own power-brake signal wire back to the rear of the truck. I'm cool with doing this if it comes down to that.

My question is: Is there a factory Ford power-brake line taped off and hanging out somewhere along the rear frame rail that I can use for my power-brake signal? I figure there logically has to be one since the Tekonsha harness carries the power-brake signal wire (blue wire) and it plugs into the truck wiring under the dash... otherwise the signal wire would just be a pigtail. Right?

So... I'm guessing it's there somewhere. If so, where should I be looking and what color is it?

Thanks in advance.

[SmokeyWren]

It sounds like your previous owner messed up the truck's wiring good and proper.

The 2004 came std with the trailer tow pkg, including a 7-wire and a 4-wire plug at the rear bumper. But not including the receiver hitch, which was optional. So all you should have to do is plug in the brake controller under the dash, and plug in the 7-wire trailer plug at the back bumper. If you trailer has a 6-wire plug instead of a 7-wire plug, you can buy a converter at any RV or trailer supply store.

If the PO screwed up the stock trailer plugs and the wiring harness to those plugs, then you're on your own to reverse whatever he did. But all the wires needed, and in the right size, should already be there somewhere near the back bumper. I don't do automotive wiring, so I would take it to my RV store and have them restore the trailer towing plugs to standard configuration of 7-wire and 4-wire plugs at the back bumper.

[svlandscape]

On my 04 f250, it was next to the spare tire by the frame rail. All your wires should be there, i.e. brake, trailer left, right turn signal, running lights, battery charge, and trailer brake wire.

They should be all marked from the factory with their descriptions. As far as I know, they are also fused seperately from the truck lights so if you have a short in your trailer wiring, it won't blow the truck fuses and therefore the lights.

You may have to remove the spare tire to access them more easily.

Good luck!

[Tungsten]

Thanks guys. I'm probably going to dig into it here in a little while just to assess the situation and proceed from there.

[94_turbo]

get the same size and color wires to repair the clowns mess, and use heat shrink butt connectors--no rot!!!! ive repaired one toooo many that didnt use them at the back of the truck--can you say major rot?? and it dont take long--

[Tungsten]

I don't do butt connectors. Solder and heat shrink only.

I did locate the factory harness for the trailer electrical. It was on a cross member directly behind the spare tire. It appears to be a 12-position molex style connector. I verified +12vdc constant on one pin, brake, RH turn and reverse lights. LH turn was either not working or giving milivolts of power rather than +12vdc. I say this because one terminal in the connector gave fluctuating but extremely low voltage when LH turn was on.

I suspect that maybe the factory harness was damaged in some way and rather than fix it properly, the previous owner removed it and then rigged it together using a 4-position trailer harness.

I just looked through my F250 service manual PDF pages that I had copied off the Internet several months ago but apparently I neglected to copy the lighting sections. Can someone here provide me with the pinout for that factory connector near the spare tire position?

Also if we've got a friendly Ford tech or parts manager here, perhaps someone can provide a part number for the harness and 7-position trailer connection that SHOULD be connected to that harness.

Thanks.

[Tungsten]

Here's the pinout of the factory harness in case someone else needs it and stumbles across this thread:


Ground .................................................. White
Trailer Battery Charge (+12v switched) ........ Orange
Trailer Electronic Brakes ............................ Dark Blue
Left Turn / Brake ..................................... Yellow
Right Turn / Brake .................................... Dark Green
Reverse Lights ......................................... Black / Lt Green
Running Lights .......................................... Brown / White

[wittmeba]

These might help.

Marksrv.com 7 way wiring diagram page

http://www.offroaders.com/tech/image...uck-wiring.gif