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Troubleshooting Trailer Wiring Harness Running Light Circuit Stays Powered Up

Question:

I have power all the time on connection for tail lights the plug in next to the ground plug wiring kit is CQT118362 installed by U-Haul. No lights on trailer work. U-Haul trailer Is this a bad new wiring harness???

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Expert Reply:

Sounds like you're dealing with a Tekonsha # 118362 on a 1998-2004 Nissan Frontier, a 1998 Nissan Quest or a 1998 Mercury Villager.

If the taillight circuit on the 4 pole connector is putting out voltage even when the vehicle taillights are switched on, it's entirely possible that the converter is blown and needs replacing. However, it could also be a poor ground connection.

Make sure that ground is attached to clean bare metal, with no corrosion or undercoat between the ring terminal and the metal chassis of the vehicle. Before I attach a ground using a self tapping screw, I like to sand down a dime sized area around the hole down to bare metal. I then place a star washer between the ground screw and the chassis, so the washer takes a good bite into the metal surface when tightened. That way, you're not just getting ground through the threads. Once secured, give the area a quick splort or rust inhibiting spray paint to protect it.

If improving the ground connection doesn't do the trick, then the converter is blown and needs replacing. This would have been caused by a short circuit somewhere in the running lamp circuit on the trailer. You'll want to trace the running lamp circuit (typically a brown wire) from the trailer connector back to the lamps, looking for pinched wires, loose connections and cracked or worn wire insulation. Anything that would allow the copper wire to short out on the trailer frame. If this isn't done before replacing the taillight converter on the vehicle and locating and repairing the short in the trailer wiring, you'll continue blowing up taillight converters, which will become annoying not to mention expensive.

I'll link you to a trailer wiring troubleshooting article that you'll find helpful.

expert reply by:
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Mike L

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