Hmm, factory trailer connector has a fault somewher - Ford Powerstroke Diesel Forum
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post #1 of 3 Old 03-29-2019, 02:48 PM Thread Starter Rookie
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Hmm, factory trailer connector has a fault somewher

2012 F350 with all original factory wiring, including bed plug for factory installed fifth wheel bracketry.

I found the problem strictly by accident. I was rewiring a small utility trailer and when finished I had no tail lights. Brake lights, turn signals work but no tail lights. Convinced I did something wrong and went about double checking all my work. Scratched my head for a bit and tested the 4 pin connector on the truck.
Found the problem was with the connector on the truck.

Long story short I checked the connections on the 7 pin connectors as well and all of them have a dead pin for the trailer tail lights. The truck tail lights work fine with or without a trailer plugged in.

The only thing I've touched electrically on the truck is installation of the AMP retractable running boards but those are wired into the door switches, although I know the tail lights also come on when the doors are opened. Could this somehow be connected to a dead circuit in the trailer wiring harness. I'm confused.

Any suggestions on where to look?
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post #2 of 3 Old 04-06-2019, 07:41 PM
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Have you checked the fuse & relay for the trailer wiring harness? In my 2013 it was the box behind the drivers side battery. I had my key on when connecting my utility trailer once and it blew the fuse for the trailer running lights. I don't recall which fuse it was but it should be in your owners manual.

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I'm having a similar issue on my 2011 F350.

I don't have brake or turn signals on my trailer. Both 7 & 4 trailer plugs aren't working. I check the fuses & relays & all appear to be fine.

I don't have power coming out of the factory harness near the back of the trailer plug. I'm wondering if there is another connection further up the wiring harness I should check.

Any thoughts on what to check next?

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