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Trailer Brakes Lock Up After Installing Replacement 7-Way Wiring Harness on a 2005 Nissan Xterra


I installed the part # 118267 on my 2005 Nissan Xterra Off Road with no trouble and all lights worked. When I tried to move the trailer, something didnt feel right and I could see drag marks in the dirt from the locked brakes. It did not show a connection on the brake controller, however at the time I thought that was a brake problem I have also been dealing with. I re installed the old wiring harness and everything went back to normal and the brake controller also showed a connection. I gave it a quick run around my neighborhood and everything worked perfectly. I have no doubt it is a problem with this replacement harness, I just wouldnt know how to trouble shoot it.


Expert Reply:

It sounds like the brake output circuit is getting 12 volts of power all the time. This could be due to a mis-wired connector or a mistmatch between the trailer connector and the new 7-Way. There could also be a bent or broken pin somewhere in the new harness or where it connects to the vehicle. And finally corrosion on the trailer connector pins can cause a short from the 12 volt pin to the brake output pin.

Lets take a look at how your trailer side connector is pinned out. I have included a diagram. If looking at the face of the connector brake output pin is located in the 7:00 position and the 12 volt power is located in the 11:00 position. The vehicle side would be a mirror opposite of this. I have included a diagram of how the 7-Way should be pinned out as well.

If the trailer is pinned out differently, this could cause the problem you are having.

Next, use a circuit tester like # 40376 if needed to test the new 7-Way WITHOUT the trailer connected. If the functions of it do not match the diagram I have included then something has been pinned wrong and you will need to open up the connector to adjust it or change the trailer side pin out to match.

If everything is pinned like it is supposed to be then check where the new connector plugs in and look for broken or bent pins, dirt, and corrosion that could be causing a short.

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