Loud buzzing when applying brake

steelshooter wrote:
Doug, There is an LED Stop light bar installed. It may not be factory but the back cap has an indentation for the light bar to recess into the cap. The response to the diode splitter sounds like what is actually happening. The noise seems to be located half way between the stop light bar and the right tail light. I believe it is in the cavity between the cap and the frame, thus I can not see from inside the camper or from under the trailer when I drop the belly cover. You are also correct about checking the system before we travel. Also if pyoung47 were to hear this in a campground he would hear it every time I put it into hit the brake to park the camper. It is actually that obnoxious.

I'd check the voltage at the lights. Plus apply 12V (not the GMC brake wire) to the cord. Do you have the noise?

Hard to image diodes or LEDs making any audible noise.

My WAG is you're hearing a backup buzzer on the camper due to miswiring.