Trailer Wiring Fault / Disconnected Warning - One Solution

[Crumgater]

After our second season running with sporadic "Wiring Fault on Trailer" and "Trailer Disconnected" alarms on the dash of our 2008 F350, we pulled into an RV Service station in Tillamook Oregon (we were 3 days into a 10 day trip down the coast), and the tech there told us it was a known problem with the truck, and "no big deal"... as far as we could tell, even with the "disconnected" alarm, all running lights stayed on and the brakes still worked, so... we started investigating the truck side of things. We had already exhausted the trailer side (or at least, we think we did).

So... after searching a bit more on truck forums, here's what we came up with:

Insufficient GROUND connection between truck and trailer frames.

About a year ago... pretty much when the problem started (in hind sight, so we think)... we added some spongy shelf liner squares between the hitch base and the truck rails, which did a great job at removing the 'clunking' we were getting while driving (and especially on starts/stops).

This extra insulation apparently insulated the hitch from the truck... and separated the grounds. From what I read on the Ford Truck Forum, trailer wiring often relies on the hitch/ball connection itself to connect the grounds together, since the ground wire in the 7-pin connector is wholly unsuitable to transmit the 20+ amps of ground current required for big trailers.

To test this theory, we used jumper cables to connect the bottom of the 5th wheel hitch (up above the king pin) to the hitch rails in the bed of the truck.

The next 200 miles resulted in 2 "fault" alarms (instead of one every 10-30 seconds) and ZERO "disconnected" alarms.

So... we think we found our culprit.

We will be inspecting all brake wiring before our next trip, just to be sure... as I see a recent post about bad brake wiring causes this same issue for another one of our members. But, that case also had trailer brake failures, which we did not experience.

Also... on Ford's... if you run through the "System Check" on the dash you can acknowledge and silence the "Ding" for the wiring fault alarm (assuming it's in effect at the time), so it won't keep chiming and driving you batty. The text still shows on the dash, so you know the error is there, but the noise goes away.

 

[Lou_and_Bette]

Dave, I had a 2008 F450 and I started getting this alarm and could not find the source until, while getting routine truck service, tech noticed "cyclops" stop light wasn't working. Turns out on same relay, not fuse, as something to do with trailer wiring. Replaced relay, problem went away.

 

[Crumgater]

Thanks Lou!
We'll add that to the check list.

 

[Jim.Allison]

Almost all DC electrical problems can be traced to a bad ground. Notwithstanding that I would look at the Ford component mentioned earlier. OR a new 7 pin.

 

[Bones]

Just a few things to add to your check list. Inspect and load check the coach battery, Ohm out the ground and brakes from the pigtail to see if you have resistance or very little resistance or no resistance. My problem came from the wires in the axle shorting out somehow. I think they were damaged. Your brake controller may be different than mind where mine shuts off the brakes but I still have trailer lights when a fault is present. Here is what my lines looked like inside of the axle.

The top wire is from the front axle The bottom wore is from the rear axle. I had to cut the top wire to get it out of the axle. When I replaced the front axle the rear one was ohming out good. It ran for 1500 miles until I hit some very bumpy off ramp and all of a sudden the rear axle went out and shorted out my whole braking system. I completely lost brakes. Had to drive very very very carefully to get home a slight hair raising experience with 15k pounds pushing you. Here is a close up picture

I'm just saying that make sure you check everything out. You could also have a bad magnet and ohming them out would point to that as well. I really don't like the idea of things rubbing along something else. i.e. the brake magnet. I think all manufactures should go to disc brakes but that is a story for another time. Good luck.

 

[porthole]

2011+ 6.7's Super Duty's still have the same issue occasionally (maybe the gas models too, but I don't follow those forums) .

 

[Jim.Allison]

Holy cow!!!!! Thanks for the warning!!!! I think I would consider cross-linked polyurethane wire for that application. This is a true fix it, even if it aint broke scenario.

Just a few things to add to your check list. Inspect and load check the coach battery, Ohm out the ground and brakes from the pigtail to see if you have resistance or very little resistance or no resistance. My problem came from the wires in the axle shorting out somehow. I think they were damaged. Your brake controller may be different than mind where mine shuts off the brakes but I still have trailer lights when a fault is present. Here is what my lines looked like inside of the axle.

The top wire is from the front axle The bottom wore is from the rear axle. I had to cut the top wire to get it out of the axle. When I replaced the front axle the rear one was ohming out good. It ran for 1500 miles until I hit some very bumpy off ramp and all of a sudden the rear axle went out and shorted out my whole braking system. I completely lost brakes. Had to drive very very very carefully to get home a slight hair raising experience with 15k pounds pushing you. Here is a close up picture

I'm just saying that make sure you check everything out. You could also have a bad magnet and ohming them out would point to that as well. I really don't like the idea of things rubbing along something else. i.e. the brake magnet. I think all manufactures should go to disc brakes but that is a story for another time. Good luck.