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Troubleshooting Intermittent Trailer Connection Error Message Where Wiring Still All Works

Question:

I have a new trailer that functionally works fine. The issue is that my truck frequently thinks the trailer is disconnected message in dash then immediately goes right back to connected. During this brief moment everything works fine - lights, brakes, etc. It is NOT anything loose, nor a bad ground. It IS the trailer - does the same thing on another truck, and a different trailer works fine on THIS truck. My assumption is that the trailer detection circuit is the brake circuit. The odd thing I found upon disassembly of the seven pin is that I only have five wires instead of the six I expected no reverse lights. The missing wire is the 12 volt wire, however the trailer does show charging when connected via a yellow LED. A little wire tracing tells me that the trailer brake circuit appears to be shared between the charging wire from the battery box and the trailer brakes. Im guessing that some side effect of that is causing my trailer disconnected message. This wiring doesnt seem right, but this is how it came from the factory. My knee-jerk reaction is to simply wire it up properly - which is annoying with a brand new trailer, but have you ever seen this? Should it work? I wouldnt think that the low voltage from the trailer brake circuit would charge the batter, but it does light up the charging indicator.

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Expert Reply:

The disconnect error code you are seeing would not be related to the 12 volt charge wire of your trailer wiring. Not every trailer has something connected to this circuit so it would be an inconsistent circuit to use for connection. Most of the time it's the ground circuit not having a solid connection that causes this error code since that's the circuit that is connected to all of the trailer's wiring.

That said your trailer brake output circuit should not be charging your trailer battery. That circuit needs to be charged with the 12 volt circuit. So that bit of odd wiring should be cleaned up and in doing so you may end up solving the odd issue. Run 10 gauge wire like part # 10-1-1 (sold by foot) to the positive post of the trailer battery to give it a maintenance charge when you are towing.

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Jameson C

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