Converter Needed for Installing RV Style 7-Way on Vehicle with Round 7-Way
Published 04/14/2025
Question:
I’m working on a 2008 gmc c8500. It has the semi round 7 pin hookup and air brakes. I have the Hayes air actuated brake controller and I’ve wired in a separate 7 pin blade connector for a regular trailer. This truck has a separate brake light signal from the turn signals but uses the same light so not sure how to wire the brake lights. I wired it normally to the turn signals but still get no brake input. Then also I have constant power to the trailer brakes. If I disconnect the brake signal input for the brake controller it still has 12v coming from the controller on the brake signal input wire. Possibly a defective brake controller bleeding over?
asked by: Jean
Expert Reply:
Hey Jean, on heavier duty vehicles like what you have the trailer wiring will have the stoplights and turn signals on separate circuits. So since you are also trying to wire in a RV style 7-way that needs those circuits combined what you would need is a converter like the part # HM48847 that you can use to get those circuits on the same wires and it should take care of your problem.
It does sound like the current dedicated stoplight circuit is ran to your brake output circuit which is why the brakes are locking up.
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Jean
4/14/2025
Let me clarify the brake locking up issue. Even if there is no brake signal input into the controller I still have 12v on the trailer brake output. I cut the input signal wire from the brake controller so there was no input whatsoever and I still had 12v to the trailer brakes. When I tested the red wire on the controller that was no longer wired to the truck it had 12v coming out of the controller. Like power was bleeding over inside the controller. Hope that explains it better