What causes "Trailer Disconnected" message?

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bmtndog

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Yes, it does. It is the type with a cylinder in a sleeve with the cylinder connected via a cable to the tow vehicle. If the cylinder gets pulled out of the sleeve, the brakes go on full. I've tested that it works.
 
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bmtndog

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Solved.

It was not poor grounding or LED lights.

I finally had a chance to tow the trailer to a dealer (2 hours away). There, we were able to connect and tow an identical trailer with the Expedition. There were no trailer disconnects. This finally and definitively pointed to the trailer as the problem.

To make a long troubleshooting session short, we found that the resistance of the trailer brakes, as seen by the truck, on the "good" trailer was about 1.7 ohms. On the "bad" trailer it was about 2.0 ohms. That does not seem like it would make much difference, but as an experiment we decided to lower this resistance by adding a parallel resistor (across the brake control line to ground).

I pulled from my EE degree 40 years ago to calculate the needed resistor should be 0.8 ohms or so. Of course we did not have a resistor that size, so we used a 10 W dashboard lightbulb.

We ran a wire from the brake line all the way into the truck cab. Then, took a couple of different light bulbs with us. While I drove, the mechanic would connect the light bulb using the ground from the 12V plug-in power port on the dashboard.

Sure enough, when we used the 10 W bulb, the trailer stayed disconnected. In fact, he could force it to "disconnect" by removing the bulb from he circuit.

Problem diagnosed.

The solution we implemented may be temporary, but it worked the entire 90 mile drive home! We simply wired a bulb socket between the brake control wire and ground underneath the trailer. Now, whenever I put on my brakes, a small light bulb is coming on under the trailer ;-) The good point is that I can pull that socket and wire in a small resistor to make a more elegant and permanent fix.
 

Betty Boop

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Hello out there. Can you help me with this same problem? Based on my own experiments, I have concluded that my 2015 Ford Expedition's towing system is made for a much larger camper then what we own. When we connect it to our 2 neighbors campers with two axles each, the Expedition stays saying the trailer is connected. But on our own 18' camper with only one wheel, the car starts out saying connected then disconnected exactly as the initial writer explained, dings and all. Unfortunately, I did not understand the solution to this problem. RV World of Nokomis, FL is stumped and not sure how to solve the problem. I'm concerned because we are planning a 2 month trip in late April to Calif and should there be any accident, how could I prove that my brakes were working and that it wasn't my fault? The liability issue is scaring us. I know the brakes are working but the legal authorities may not understand.
 
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