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7 Way Trailer Connection Troubleshooting


2017 mack gv713 dump truck. I bought a new dump truck and its wired like a semi would be with air brakes. The problem I have is all my trailers are electric and run on a standard plug or rv plug I guess its called? I had a friend that works with brakes and wiring put a brake controller box and change out the plug from a 7 way round pin plug to 7 way flatrv style plug. I have turn signals, running lights and electric brake is working but no brake lights on trailer? Do I need to run wire from brake lights or turn signals of truck to one of the wires leading to plug on truck or what? Thanks in advance for any info.


Expert Reply:

Yes. It sounds like there is no signal being sent from your 7 way connector to your trailer, or it is not being received for the stop and turn lights. I recommend using a circuit tester like # PTW2993 to check the functions at your truck first. If you are getting signal on the posts on the truck you know the problem is in the trailer wiring, and if you are not getting signal there, you have isolated the issue to the truck first. You will need to splice into the wires at your tail lights to get your brake light signal and your reverse light signal. I suggest using wiring like # 119190 to combine your lighting like a standard trailer needs. It sounds like you are missing your 12V power as well. You also want to make sure you have a solid ground for your trailer too.

I've attached a photo to help.

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