Troubleshooting Voltage Drop to Trailer Brake Assemblies
Updated 11/20/2025 | Published 10/06/2018
Question:
My RV has dual axel electric brakes. The brakes we operating poorly low grab if you will, so I took unit in to fix. We put on all new backing plate with new pads and new magnet and arm assemblies. Once back together, the brakes worked identically bad to prior the change very low grab. Even pulling the brake away pin resulted in very low grab trailer would move with truck in neutral while on a slight downhill incline. We tested wiring and voltages all over the unit. We found the brakes cause a very large in voltage at the brakes. While we have 12.5 volts at the brake controller, and 12.5 volts in the RV control box, we are only getting 9.5 volts at the brakes. We tested each brake while isolated and each would draw down voltage about .6 volts. We hooked unit up to a different truck, and got same results. We hooked the RV to shore power, and got similar results 13.7 V at the control box and only 11 at the brakes. We tested each brake independently on shore right at a battery, and each used 3.5 amp and ped voltage only about 0.1 volts. We ran #12 wire from the control box along the outside of trailer directly to brakes and got same Volt . Could this be from a bad battery inside the RV, pulling charge or something? We are totally stumped as to how to get full power on the magnets so they grab.
asked by: Paul
Expert Reply:
I believe you almost solved the problem when you swapped the wiring, but in reality you needed to use 10 gauge wire like part # 10-1-1 (sold by the foot). You are experiencing a voltage drop due to the long distance of wire that's not thick enough. Replacing all of the wiring on the power circuit and the ground circuit will allow the brakes to have the amount of voltage to apply. I'd run all of the ground wires back to to the main ground harness of the trailer wiring as well.
It's also possibly your magnets are in need of replacing. If you check out the help article I attached you'll see how to troubleshoot them.
Bryan J.
11/20/2025
I am also having the same problem, 11.8 v all the way to the brake assemblies and when I hook up the brakes drops it down to 6.8v. I’ve got all new brake assemblies and ran new wire and even ran an extra ground but still getting a big voltage drop
Jameson C.
11/20/2025
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on Wiring
Patrick
11/16/2024
I have this exact same issue and I upsized the wire to a #10 wire. The voltage increased a little but when i applied the breaks still at roughly 6 volts. I'm at 11.6 volts all they to the first connection before I hook up the first brake. Any suggestions?