2019 Transcend 27BHS Brakes Don’t Function with New GMC

[familytruckster4]

Here is another data point that may weigh in your trouble-shooting. A few years ago, I decided to replace the brake lights on my 2017 Reflection travel trailer with LED bulbs vs. the original incandescent bulbs. They worked great for a while. But one day, while applying the brakes, I got a message on my Fords display that said "trailer brakes disabled". It was intermittent at first, then happened more frequently as time went on.

So I went through a ton of trouble-shooting to try and resolve it. I rewired all the grounds to a central buss terminal and replaced the 7way connector and junction box. I spent a ton of time trying to resolve the problem to no avail. Then it dawned on me. I remembered the LED lights. So I changed them back to incandescent. That was it, the problem never reappeared and the interaction between the truck and the trailer is still fine today. After much discussion, it was determined that the LED lights had much lower resistance than the incandescent bulbs. This tricked the truck into thinking there was a fault. There was nothing wrong with the truck, but it wasn't designed to accept the low resistance of LED bulbs.

This could be the issue with your combination also. If so, I believe there are resistors or adapters to help resolve the problem.

Jim

Youre issue is fairly common, on some of the newer trucks the control module for the trailer has to see a certain amount of resistance. As you said, A resistor wired into that circuit will fix it. Its the same reason replacement LED on other vehicles will hyper flash when used in place of incandescent lamps.
I know that the electrical architecture has changed a few times on the GM trucks. I believe the HD trucks changed in 2020 and the new 2024 HD's are another version.