Repaired Intermittent Power to Electric Trailer Brakes

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As we started our snowbird journey south, we ran into a hiccup on the first day in the USA. After crossing from Victoria, BC, to Port Angeles, Washington, we were heading down Highway 101 along the Hood Canal when a warning message appeared on the dashboard. “Check Trailer Brake System”. Also, “Service Trailer Brake System” and “Trailer Brakes Disconnected.”

I pulled over and checked the 7-pin tow cable connection. All pins looked good, and it was firmly plugged in. I continued, but again, intermittently, I’d hear a warning chime, and the messages would pop up. Each time, I’d lose trailer braking power! So we pulled into the nearby Little Creek Casino and paid for three nights (only $15) in the dry camping dirt lot. That would give me time to diagnose the problem.

Little Creek Casino

I posted to social media that we had trailer braking problems and thankfully got several comments and emails with tips about the possible causes. The most likely to me was chaffed wiring running through the axle tubes. The wires bounce and move inside the rough steel tubes until the outer covering wears through, exposing the copper wire and intermittently short circuits power to the frame ground. The short circuit triggers the truck’s computer to issue the warning and turn off the brake controller power.

testing for short

After inspecting the wiring, I noticed the rear axle wiring copper was blackened, likely from overheating due to the short circuit. I pulled out the axle tube wiring and, sure enough, spotted some chaffed spots exposing copper. So, I ran a temporary bypass wire by sacrificing an extension cord. I figured that would do the trick.

Wrong! After traveling a bit further down the road, the messages and loss of braking returned. So we pulled into the next rest area, and I pulled out the front axle wiring. Again, I found the chaffed areas, and a few were even worse than the rear, with copper threads hanging out. I once again bypassed with more extension cord wire.

chaffed wire

undercarriage axle wiring

I’m happy to report that it solved the intermittent trailer braking problem. We drove over 4 hours yesterday with no messages and good braking power. Once I’m down south, where it’s dry and warmer, I plan to run new wiring. Rather than through the axles, I’ll run it up through the trailer underbelly, where it will still be protected from the weather and road debris.

Intermittent Trailer Braking Diagoses & Repair Video

Upgraded Electric Trailer Brake Wiring & Adjusted Brake Shoes

In this video, I installed new wiring across the axles of my Keystone Cougar fifth-wheel trailer. The old cross-over wiring inside the axle had chaffed and shorted out, causing issues. I also adjusted the shoes on the Dexter electric brakes and replaced what I mistakenly thought was a defective star screw adjuster.

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Intermittent Trailer Brake Repair

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