12v Constant on Trailer Plug?

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ScubaSteve
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Model Year: 2016
Location: Kansas City, MO

12v Constant on Trailer Plug?

Post by ScubaSteve » Wed May 13, 2020 4:25 am

Its a long story regarding the grand incompetence of multiple parties, but suffice it to say, I had to replace the main chassis harness in my truck leading from the bulkhead connector in the driver's fender well to the rear of the truck.

That being said I found the replacement harness to be defective in that the 12v Aux pin and the parking lamp pin in the 7 pin trailer plug connection had been placed incorrectly (I had to swap the two wires). Now that I have corrected that, my concern is that the 12v Aux pin has a constant 12v feed, even with the truck off. So with that, might I ask if someone would be willing to go test the number 4 pin in the attached diagram and see if it has a 12v feed with the truck off? I am finding conflicting info as to whether it should be switched or if it should be constant.

Thanks in advance!
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7-Way-RV-Style-Trailer-Plug-Wiring-Diagram-1.png

EasyDoesIt
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Re: 12v Constant on Trailer Plug?

Post by EasyDoesIt » Wed May 13, 2020 6:00 pm

Confirmed, 12v power at pin 4 when vehicle is off.
Live: Las Vegas NV, Drive: 2018 PW & 2014 LR4

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Mule
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Re: 12v Constant on Trailer Plug?

Post by Mule » Wed May 13, 2020 6:22 pm

yeah, that one's always-on.
Fords put that pin on a relay so it's only on with ignition.

I ended up putting a switch in my trailer to connect/disconnect that pin to the trailer. Lets me isolate the truck so I don't kill its battery with the furnace/lights, but I can still charge the batt on the way there or back.

ScubaSteve
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Re: 12v Constant on Trailer Plug?

Post by ScubaSteve » Wed May 13, 2020 6:54 pm

Sweet. Thanks a lot!

RustyPW
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Re: 12v Constant on Trailer Plug?

Post by RustyPW » Wed May 13, 2020 11:06 pm

On my motorhome. It's only powered with the key on.
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