Trailer brakes stop working when headlights are on

Sorry, for not providing any updates as I was in the process of moving my daughter into college and getting her settled in. I tried several different testing methods including looking for a bad ground, connecting a separate ground from trailer to truck, hooking up another truck to see if it had a similar issue and even having a mobile RV tech come look at the issue. No luck! Appears it may be an issue with the IBC itself.