Trailer brake electrical connection warning light

[Als]

I would be checking and cleaning grounds.

[pawpaw]

You might also check the connection between the trailer 7 prong plug and and your truck. I've had it happen where corrosion built up over time and caused a problem. Now, I clean the electrical connections at both ends and use a dielectric grease to prevent further issues. So far, no other problems to report.
Good luck

[kuba122]

I have noticed that the connections under the trailer tend to be a little sloppy compared to those under a car ..... Intermittents are not easy to find. Look behind the wheels on both sides, the wires you see going to the wheel hubs are the brake wires, check there, first, just because it's easy. One wire is hot from the controller, the other is a ground. You have to check both. You may end up following the brake wire from your controller through your TV then through your trailer.

[Greybeard52]

I keep getting a message on the dash of my truck that my trailer brake connection is not connected. It comes on intermittently as I drove 600 miles up to and returned from Wyoming where I live to Montana last week. I was going up and down steep hills and the brakes seemed to be working and my trailer lights were on. I cleaned the connection between the trailer connection and the truck with electrical cleaner. Any ideas about what I need to look at next?