Troubleshooting Trailer Brake Wiring and Truck Connection Issues

Updated 07/28/2020 | Published 07/27/2020

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Question:

2018 2500GMC w/ trailer brake system. Service and check wiring alarms come intermittently on dashboard. Have completely rewired trailer, removed charger and trailer battery, still no brakes. Trailer is wired perfectly. Only thing not replaced is the main 6 conductor cable, which all ohm out to 0 from end to end. Connected a second trailer to truck and it works perfectly. Connect subject trailer to alternate truck and it dont work. Each brake has been separated into its own circuit, one cable per wheel w/ fuse in each circuit. One hot wire to all fuses to each brake and all negatives wired back to negative of trailer. All grounds are consistent. Each brake has 3.4 ohms w/ fuses open, when I close the fuses, the ohms to 1 ohm when all 4 are connected. I have been in the controls business for over 30 years and this is kicking my butt. Need help. What is the truck looking for in the brake system to make the determination that something is wrong?

asked by: Jim A

Expert Reply:

You have definitely determined the issue is on the trailer because another trailer on that truck works, another truck and that trailer still doesn't work. You have done a great job of checking each individual item, the issue is the drop when you close the fuses. You need change your wiring on your trailer brakes. There should not be separate circuits for each wheel and the issue with the truck is it is looking for a power draw on the brake controller output pin connected to your trailer brake wires that isn't enough of a draw the way you have it configured. I have attached a help article on the wiring you need on your trailer brakes which doesn't have any additional fuses or circuits. Simply use wire like # 10-1-1 to give you the wire you need (sold by the foot) to deliver power and also the ground to your axles.

expert reply by: Jason S