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-   -   Help! Truck Fault Causing 100% Braking of Trailer!!! (

Aufgeblassen 07-13-2014 11:47 AM

Help! Truck Fault Causing 100% Braking of Trailer!!!
We got our 2007 F-350 6.0 (w/towing package) and 5th wheel RV a year ago. Right from the get-go, I would get the dashboard message: CHECK TRAILER, and most of the time, it was there very momentarily, after hitting a bump in the road.

Once in a while (not very often at all), the message would remain solid, and I'd have no trailer brakes, so I'd pull over and unplug & reconnect trailer cable on side of bed, and all would be good.

On a current trip from FL to CA, in east Texas the trailer brakes would go to 100% application with the lightest of braking (apparently whenever brake lights were activated), and the message: TRAILER FAULT would appear on dashboard. The trailer brakes even came on 100% whenever turn signals or 4-ways were on!!! (i.e. whenever light(s) for them on dash were ON).

The problem suddenly stopped (thank goodness before we went thru a thunderstorm). The next day, problem was back & then stopped again. The next two days on the road, problem did not happen at all.

While here in LA, while driving around (without RV), I began having TRAILER FAULT indication on dash (whenever applying the brakes), meaning problem was with the truck, not the trailer.

BTW: My normal trailer brake application setting is "8" (out of 10), but when I turned it down to "0", trailer brakes still applied just as hard during the fault condition.

BTW II: I check my OBD II with my smart phone, but no errors show up specifically about trailer.

Any ideas? :(

I just found out there is a recall on the ignition switch whereby brake light may not work due to a problem with it. Could that be the problem???

Aufgeblassen 07-13-2014 06:37 PM

62 relies & NO responses.

Come on!!! I am far from home, an :-downd don't know what is going on!!!

senix 07-13-2014 08:59 PM

I think your problem is at the truck side connection. The plug probably has loose or dirty connections.

I would start there by taking the plug apart and inspecting/cleaning and tightening the connections.

I am going to move this thread to the towing section for more assistance.

jdadamsjr 07-13-2014 10:22 PM

as senix said -
start at your bed side connection and work back the wires to the hitch connection were it is plugged in...
pretty easy to check since it is probably plugged in right by the rear hitch...

check for continuity and/or open wiring... guessing it's chaffed wire or bad connection somewhere...

if whomever put the bed side connector in did not protect the wires in anyway, they could be the culprit...

if not there, trace back further for continuity and or bad connections...

if you are on the road, consider going to the campground office to find a local tech / dealer - that's not something to drive round with a 5er attached!

RV_Tech 07-13-2014 10:56 PM

This is an unusual situation as it is not a trailer disconnect issue. I don' think this is wiring issue. I think it is controller problem. The reason I say that is you know you have continuity on the brake line as you have too much rather than not enough brakes so you have plenty of current. The wiring has to be connected and intact or you could not have such severe brake activation.

It sounds to me like the controller has lost it's ability to properly interpret pedal pressure and deacceleration. I would take this to a Ford dealership to check the controller. A tech or RV dealer can verify you have too much current with minimal pedal activation, which you already know, but will not be able to test the controller further.

My two cents worth,


Aufgeblassen 07-14-2014 12:34 AM


We noticed there is no center pin in bed sidewall socket, as compared to the socket on the bumper. Removed connector from bed sidewall & took apart, and found on inside of connector was a loose hex threaded standoff, that used to be connected to a center contact. Said standoff was apparently bouncing around and shorting wires!!!

Thanks, everybody, for your help!

senix 07-14-2014 06:05 AM

Glad that the connector was the issue.

Now, make sure they are all clean and put a little grease on them to keep them clean.

any more issues then I'd look at the controller.

David7.3 07-14-2014 06:25 AM

That center pin on the 7 way is for reverse lights, FYI. loose wire in the female connector would def. give you all kinds of trouble, it could also short out the controller too, seen it happen.

RV_Tech 07-14-2014 06:54 AM

Here's the part I don't understand on the fix. The center pin only goes hot when reverse is activated. It can feed back to the controller if it shorts to the hot for the brakes when reverse is activated, and that would give the "trailer fault" message, but otherwise there should not be any power down it unless there is a problem with the reverse signal. That pin should not be hot at other times. I don't get it.


David7.3 07-14-2014 07:06 AM

If the standoff was out and bouncing around, there is a hot lead in the connector at all times the truck is running, (to charge trailer battery, ect.) you know how tight it is in there, it is possible that it dropped down and touched the trailer brake connector which is at the 5 o'clock position, it may have touched some others but ho would not have noticed if a turn signal or something else was touching, and after bouncing around he did say the system did work!

RV_Tech 07-14-2014 07:22 AM

Okay, I think I understand. The wiring at the receptacle reverse was just providing a pathway for shorts to occur. I missed the part in the initial post where turning on the four ways or anything to do with the brake lights would activate the brakes. That, along with the "check trailer" warning could certainly account for the messages.

Two different messages; "trailer fault" is saying "hey, there is power on the brake feed that shouldn't be there" or short some place, "check trailer" is saying "hey, we lost connection with the trailer". Oops on my part! :(


David7.3 07-14-2014 07:49 AM

Job well done

Aufgeblassen 07-14-2014 11:18 AM

I guess since I don't have reverse lights anyways, there is no need to replace connector. :-X06

senix 07-14-2014 11:35 AM

Replacing the connector is not needed if you repaired it and the issue has gone away.

SpringerPop 07-14-2014 02:35 PM


Originally Posted by Aufgeblassen (Post 14506031)
I guess since I don't have reverse lights anyways, there is no need to replace connector. :-X06


In a half-fast sort of way, that would be OK.

That which you do,
do with all your might.
Things done by halves,
are never done right!


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