Troubleshooting Brake Lights Blowing Fuse When Connected to Trailer

Question

Question:

I have a similar problem to another I saw on the q and a. All my lights work fine, turn, running, and even hazards work just fine, but when I mash the brakes it blows my brake fuse every time. All the other functions remain in working order, and when I replace the fuse my tow vehicle brake lights work again as long as I dont plug the trailer in. I have even tried leaving the turn/brake wires disconnected on the trailer and it still blows the fuse. I have plugged the trailer into another vehicle and it works perfectly. So the problem must be with my vehicle. I have a plug that has LEDs on it to tell you that it is working properly and all LEDs are working correctly until I hit the brake, then all leds go out. This is when I dont have it plugged into the trailer. Any thoughts? I am a electronics tech for 30+ years, and this one has me baffled.

asked by: John B

0

Expert Reply:

Based on your LED tester results and the fact that the trailer works fine with another vehicle we at least know that the issue is somewhere on the tow vehicle. If you can tell me what model vehicle you have along with the type of trailer harness that was installed (or if it's factory) I should be able to offer some more specific troubleshooting steps but in the meantime I first recommend inspecting the connector itself at the rear bumper. Check for any corrosion or debris that might be built up around the pins that needs to be cleaned out. Corrosion can sometimes bridge a couple circuits together causing a short.

This might be difficult depending on the type of trailer wiring you have but the next thing you will want to do is try and trace the brake/turn signal circuit wire coming from behind the connector as far as you can, looking for any exposed or damaged portions that need to be replaced.

Also, can you tell me if you are using a brake controller when hooked up to the trailer? If so, make sure you have it wired directly to the cold side of the brake light switch behind the brake pedal and not to the actual brake light circuit on the trailer harness.

Please let me know what you find and we can go from there!

expert reply by: Chris R

0

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Troubleshooting Brake Lights Blowing Fuse When Connected to Trailer

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