Loud buzzing when applying brake

wnjj wrote:
The box probably has relays inside and from what I’m reading online, it’s possible that 2019 and newer GM trucks may be sending PWM (pulse width modulated) signals on the lighting circuits. That would cause all kinds of havoc with relays connected to the line.

There are people having issues with backup cameras powered from the running lights.

You may have to replace the box with a solid state equivalent.

This was my guess as well. Not much you can do to get around it.
Take a video of the tail lights while it's buzzing and you may be able to see them flicker.

The box probably has relays inside and from what I’m reading online, it’s possible that 2019 and newer GM trucks may be sending PWM (pulse width modulated) signals on the lighting circuits. That would cause all kinds of havoc with relays connected to the line.

There are people having issues with backup cameras powered from the running lights.

You may have to replace the box with a solid state equivalent.

steelshooter wrote:
Doug, Was able to find the box causing the buzzing. Looks like something you were refrencing. The box does split the stop and emergency lights to make the 3rd stop light work. I dont really know why it is there, I am not seeing it on new campers.It doesnt look like GM is going to be able to tell me what was done to cause this to happen with the new truck. I am either going to have to put up with it or rewire the lights on the camper.Thank you for responding. Larry

It is there, because if NOT INSTALLED, every time you turned on the Left or Right turn signals, the center Brake light would come on and flash also. The diode "Sees" that BOTH left and Right brake lights are engaged at the same time and then routes the 12 volt signal to the center Brake Light. If it only sees 1 turn signal, it knows to not power the center light. Read This link for better understanding. Doug

https://www.etrailer.com/Wiring/Tow-Ready/118158.html

Doug, Was able to find the box causing the buzzing. Looks like something you were refrencing. The box does split the stop and emergency lights to make the 3rd stop light work. I dont really know why it is there, I am not seeing it on new campers.It doesnt look like GM is going to be able to tell me what was done to cause this to happen with the new truck. I am either going to have to put up with it or rewire the lights on the camper.Thank you for responding. Larry

CA Traveler, Apply 12 volt is not a bad idea, but as stated before this does not happen when connected to earlier model trucks. I had a 2013 that i pulled the camper with for 6 years with no noise. I dont think it is a back up buzzer as it did not buzz while backing on the other trucks. My dad pulled the same camper with a 2006 GMC my 2013 was a Chevy and I just tried a 2019 GMC Denali, like mine except mine is 2020, and it worked as expected. I am still working on the tail light question. I started removing the rubber around the tail light but didnt know if the light would fall into the end cap since I did not see any screws holding it. Thanks for the WAG though.

Also normally equipment can be reached for maintenance. Have you remove the stop lights to check?

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.

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.

pyoung47 wrote:
I think I can speak for the majority in saying I haven’t been inside the camper when the brakes were applied.

The OP was doing what most do NOT do. He was checking out the RV systems BEFORE he traveled and heard that buzzing. He then went inside to determine where the noise was coming from. Doug

I think I can speak for the majority in saying I haven’t been inside the camper when the brakes were applied.