Gents, recently picked up a 2009 F150 supercrew max tow with the Ford factory trailer brake, and have some reason to suspect my issues are only with the truck, and not with the trailer, but would like to hear your thoughts.

When connected to the trailer, the trailer lights all work, the brake lights light up both with the brake pedal and with the manual brake controller slider. Everything visually looks good, however:
1) the trailer brakes are not grabbing, and they grabbed fine last fall with my previous truck.
2) the truck dash display says "trailer disconnected" when I use the brake controller slider.

Trailer batteries are fully charged and battery disconnect switch is turned on.

When I hook up my 7-way tester to the truck, the LED for the brake light glows only dimly when the truck brakes are pressed, but goes brighter when the brake controller slider is pushed.

As I said I strongly suspect the issue is on the truck somewhere, as I just bought it, and it's quite high mileage (289,000 kms). It also has some intermittent issues with the rear parking sensors, so maybe the wiring under the truck has been damaged somewhere? I took and look and didn't see anything, but that's not much of a check.

What is my first step diagnosing this issue?

 

Not sure if it's relevant, but did need to replace a fuse under the hood to get this far. One of the 20A trailer light circuit fuses was burnt. It didn't burn out after all this messing around, I checked that.

Possible a wire under the bed is exposed and shorting out with something?

 

When's the last time you had the trailer brakes inspected? Might have wiring issues or a magnet that's bad

 

Inspected? Never. They worked flawlessly in the fall when I used this trailer last, but that was eight months ago.

The "trailer disconnected" message on the truck dash makes me think this is a truck issue. Is that a reasonable assumption?

 

I would try and hotwire the trailer brakes and spin each wheel to rule out the trailer.....or hook up a known good truck and see it it has the same results.
do each of the brake assm have there own ground wire going to them?

 

If you have access to another truck to test the trailer connection than I would do that first.


Secondly I would take the 7 pin plug on the truck apart and clean/inspect the connections.


The dim light vs bright light is probably due to the progressiveness of the TBC. It is designed to put out a small amount of power at low speeds and then more if traveling.

 

I am having almost the same exact issues. With the exception of the "Trailer Disconnect" message.

I noticed that is I use the manual brake slide the test light lights brighter than with the brake pedal being applied. If I hook up to my 5th wheel and set the gain to 10 then apply the manual slide at an idle it will stop my trailer from rolling in about 15 feet. However, if I give it a little acceleration the trailer will move forward and not lock up the tires.

Tomorrow I will hook up to two different trailers, a utility and a enclosed trailer and check the results. Then if needed I will have my brother in law drive over and hook up to my 5th wheels and check the trailer with his truck.

In the mean time if you find a fix let me know. Push comes to shove I may get to use my ESP to check out the truck.

 

Well, I hooked up a different truck to that trailer and trailer brakes operate fine and the truck can "see" the trailer fine.

So my issue is in the truck. That's what I suspected all along, but nice to confirm.

Tracing those wires under the bed to find one that's rubbed through the insulation or something sounds like a nightmare. Ideas?

 

start at the 7 pin connection. Take it apart and have a look.

 

well, bright an early this morning I took apart the 7-way connector. Snapped the little clip that holds it in AND the tab that you press down before removing it. Between eight year old weathered plastic and my ham-fistedness it was an inevitability.

Got frustrated and stressed that I'm supposed to be towing tomorrow morning and took the truck to a dealership for some diagnostics. They didn't end up telling me much aside from the fact that there was some visible corrosion in the 7-way and the clip was busted off... Suggested a new connector, bracket and wiring harness, at a parts and labor cost of around $700. I declined.

While they were spending the time doing that brilliant diagnosis, I had time to think calmly and decided I was fully capable of installing a new universal 7-way connector. Found a local store that carries them, and they also carry handy 7-conductor wires to rewire the truck for just this kind of purpose.

Bought a new 7-way, and installed it in just under an hour. Have it hooked up to the existing truck wiring right now, and once I get my children to bed, I'm going to test it on the trailer. If that doesn't work, I'll be re-wiring to somewhere further forward on the truck. I guess somewhere on the firewall or fusebox or something. Will need to figure out where the best spot it.

So far, paying the dealership for an hour of diagnostic work was a total waste of time, but I feel like I'm on the right track now.

 

I feel the 7 way was your orginal issue.


Did we check all the fuses already?

 

Well, lo and behold, the new 7-pin fixed it.

If I would have just done that in the first place I would have been done ages ago. I have a mental defect that makes me hate to replace parts until I'm sure exactly what the problem is. In this case, it didn't help me, and actually ended up costing me significant money.

Oh well, lesson learned.

 

thanks for reporting back. Usually it is the 7 pin that is causing the problem.


More often then not it is the truck connection.


Then there are the wires for the brakes on the trailers. The wires are pretty exposed outside the drums going into the axle tubes.

 

Worked well on a tow this weekend. I think the trailer brake are wearing out, as they don't grab as hard as they used to, so maybe I'll check those out when I get some time. But working decently for now.