Can 12V Auxiliary Wire on Trailer 7-Way Be Used To Power Trailer Brakes

Published 12/05/2019

Question:

The 7 way trailer plug has an auxiliary terminal. Can I connect it to the electric brake in a 7-4 combination for electric brake signal?

asked by: Gary S

Expert Reply:

The auxiliary or back-up wire on a 7-way trailer connector like # HM20041, is used to power to things like interior trailer lights or other 12V accessories. It can also be used to power backup lights, but not many trailers are equipped with those.

There is a dedicated brake wire (typically blue) on your 7-way trailer connector which runs back to each of your brakes. This is the wire you want to connect to the corresponding brake wire on your vehicle's 7-way or 7 and 4 way like # 37185. If nothing is connected to this wire, there is no signal being sent back to activate your brakes.

I've attached few diagrams to show you the typical functions of a trailer's 7-way as well as a link to the full FAQ and a video resource for you to check out at the bottom of the page.

If this is not what you were trying to do, feel free to provide more detailed information and I will be happy to address any additional questions.

expert reply by: Carla M