Truck = 2004 F-250, 6.0 PSD.
Auto transmission, and I noticed when putting it into reverse it wouldn’t actually go into reverse immediately.
Next I noticed that while in Park and stepping on the brake pedal, the speedo is actually measuring ~10mph!
A RV/Camper dealer wired my Tekonsha Prodigy Brake controller last winter, but I didn’t actually mount and plug it in until a couple weeks ago.
Don’t know that I’ve used the truck since I did that (or at least didn’t notice these issues).
With that in mind, I removed/unplugged the brake controller, which seemed to make the issue go away…

I need to test this further, but though I’d throw a post out here, for suggestions from those with experience.<O</O

Does anyone have suggestions or similar experiences?<O</O

 

Question.
When the brake controller was installed did the tech use the factory brake controller wiring harness, or did he tap into the existing wires on the brake pedal?

 

I think that he spliced between the Ford supplied controller harness (plug with wires), and the harness that came with the Prodigy (again, just a plug w/ wires).

Also just got off the phone with Tekonsha... they are suspecting a short somewhere in/near the trailer connection.

 

For a few bucks and a better, more reliable install, I'd use the Ford-specific harness that Tekonsha makes for the Prodigy...



It just plugs right into the six-pin Ford trailer plug behind the dash. Remove the big rectangular quick-release panel under the steering column and look to the right. You'll see the gray harness plug through that little "window". It's held in place with a plastic push-connector, but you can grab the gray plug and pull it out some to aid in plugging in the brake controller harness.



TX

 

TXHillCountry, thanks for the suggestion.

I'll have to dig into this tonight or on the weekend, to see if I can figure out where the problem is coming from...

 

This is making me kind of crazy…

Tested with another prodigy controller (new), and the speedo still bounces.

Good solid ground (straight to negative post on the battery).

Everything looks right and it still continues it’s random misbehavior.

If I unplug trailer wires from the harness under the back of the truck, near the spare tire, the problem still occurs. Leads me to believe that the last section of harness, and trailer connection is fine.

If I unplug the harness which leads to the trailer connection from under the hood (comes into a plug on drivers side, near the firewall and fender), the problem seems to go away. Not sure how something could be wrong here as all the wires in this bundle are well wrapped and run along the frame rail. I can’t see any damage after a fair amount of time crawling around underneath…

Anyone have any more suggestions?
Next steps?

 

How 'bout the pigtail from the controller to the truck wiring...maybe they send wrong one?

 

It sounds like there is a broken wire in the harness, or some kind of bleed over from the trailer break wire.
You can run a new wire from the break controller back to the trailer plug and see if that fixes the problem or replaced the wiring harness from the firewall to the back of the truck. It is a straight up job except where it runs behind the fuel tank.
You can force it through but the easiest way is to drop the fuel tank and do the harpoon mod in the process.

 

I agree, something is bad in that one stretch of harness.
I suspect that running a new brake wire (and maybe a new ground also?) will remove the problem.
That's probably going to be quicker and cheaper that a new harness, and provide the same results.
Plus I think I could squeeze these through without dropping the tank.
I do like the sounds of the Harpoon mod, but I've been dealing with the foaming since this truck was new...

 

Got a call from the RV dealer late yesterday, checking on me to see if I had found the problem...

I explained where I was at in my diagnostics and the tech reminded me of a situation he had described when I had stopped there last week... "yup, sounds like the same deal, it took forever to track the problem down on that Ford!"

It was a ‘02 SD that had developed a short in the section of harness running along the frame rail...

 

And I bet it's in a place you can't get to

 

That's almost a guaranteed situation!

Noticed that there was another recent thread related to trailer wiring...