What causes "Trailer Disconnected" message?

[bmtndog]

LED lights on the troublesome trailer. Normal lights on the trailer that worked.

We also wondered about the LED lights, but they don't dim when this happens (from the perspective of a following car), all connections are good, no significant voltage drop when standing still...

 

[Bedrck47]

Well the only thing to do would be to try on another trailer that has LED lights and see if it happens there also.
Compare apples to apples so to speak

 

[bmtndog]

Based on some info from Ford, the problem can only be with the brake controller wire or ground (below), so that rules out the lights.

Every 4 seconds (when not braking) the TBC module sends a voltage pulse to pin 3 of the 7-pin trailer tow connector to determine if a trailer is connected to the trailer tow connector.

Current thinking is that one or both brake modules is "bad" in that underway, when the tires are spinning, the resistance is high. Can't explain that yet, but I am taking the trailer to the trailer dealer in a few weeks (multi-hour drive one way). And, he thinks he has a way to test for this.

 

[Bedrck47]

Thanks for the update

Still would be interesting to know what would happen if you hooked to another trailer that has led lights

 

[Bedrck47]

Strange Look at a trailer connector wiring diagram Pin 3 is for the trailer lights?

 

[Bedrck47]

Another question for you Was the connector on the trailer a 7 pin connector or a 4 pin connector and did you use a 7 pin to 4 pin adaptor

 

[bmtndog]

Okay. That is weird. I did not think to verify that pin 3 is to the brakes! I just assumed it was. Bad assumption. So, we are back to the theory that the LED lights may be the issue. I am hauling the trailer back to the dealer in January sometime where they have more trailers we can pull to test.

The trailer has the 7-pin connector.

 

[Bedrck47]

The pic I posted may be wrong Ford wiring diagrams show something different in the pin connections

 

[bmtndog]

I think the pin numbers are different although the locations are the same. The Ford manual shows "3. Blue" = "Electric Brakes", even though the photos I've seen online call this pin 2 on the connector. So, I think it is important to go by the color code, not the pin number. Doing that, the Ford TBC sends a test voltage to the "blue" wire every 4 seconds. Again, likely eliminating the LED lighting as a culprit.

 

[Bedrck47]

When you find the cure Update the results as it will help others