If it's happening with two tow vehicles, the problem has to be with the RV. Are you sure you don't have a ground problem? It's not always the positive...

Rob

If you aren't blowing any fusses in the tow vehicles, I would not start pulling wires out. If you don't get the error message until after you've made it down the road a piece, I would start by check that my connections are in place properly connected, and tight.

If you don't blow any fusses, that's a good sign that you aren't having a short anywhere in that circuit. I would think the wires should likely be fine.

I might have a helper press the brakes while I check for 12V at every connection. While you watch your multi-meter, jiggle the connector to see if that opens the circuit.

I would start by putting my probe on the "Brake" contact of my bumper connector and reach up under the bumper and jiggle the wiring harness all around while watching the meter. Continue checking everything back from there, one connection at a time until you find something.

My bet is it's just a loose connection. It could be the piece crimped onto a wire, or that piece not fitting tight into the other connector. This means you need to make sure you actually get in and across each connector. It may take you a little time to find it. The up-side is you'll know more about your electrical system than you did before.

I hate to think it Joe, but my guess your shop may not have sorted out things reasonably well enough.  Intermittent electrical problems are the worse ones to have.  And my experience is we are all certain to meet a bad crimp job sooner or later.  Those crimp-on spade lugs are a plaque on mankind.  Of course I'm just guessing that's what type of connectors are used.  I honestly don't know.  But if you do have them, do NOT try to crimp one tighter!  Just replace it.

Good luck,
Dave

-- Edited by Dave MW on Sunday 2nd of February 2020 03:07:19 PM