Constant Hot Wire

Hi guys, I hope i am posting this in the right section, if not feel free to move it wherever mods. I have a 2005 superduty and just recently bought a gn horse trailer. The trailer is equiped with lights in the dressing room up front and loading lights in the rear. When the trailer is hooked up to a 2006 dode the lights work, but when hooked up to mine they dont. My question is how do i hook up a constant hot wire (im using a 7 pin flat connector) so my lights will work? I thought they came from the factory set up but i guess not.

THanks for the help

It should have hot at all times on that plug.

Have you used a DVOM to test the fuses? Or tried it on another ford?


Someone with experience with that year can add better insight.

I checked two of our trucks and none of them were hot on the aux pin. Although the 550 had 5v on the brake pin, which I assume is for detecting the trailer being connected.

Maybe it's something you have to connect to 12v yourself.


On Edit:

For reference,

I havent tried it on another ford. I did a visual on the fuse and it looked ok (not fried) but im not 100 percent sure i was looking at the right one. I used a tester light on the plug and nothing was constantly hot.

Ya, and i took the tester to my buddys dodge and his positive pin was hot all the time even with the truck off.

The AUX 12volt on my 7 pin only works if the key is in the run position. 02 F250.

Denver said:

The AUX 12volt on my 7 pin only works if the key is in the run position. 02 F250.

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I'm noticing that this seems to be the norm.

We have 6 superdutys and they are all like that.

That would make sense, I had an older trailer that i had to have my key turned on to get the lights to work. On the new trailer with the keys on the lights still dont work, im wondering if i blew a fuse on the truck (havent tested the aux pin w/ key turned on). Does anyone know the number fuse im looking for?

Bigdeere said:

That would make sense, I had an older trailer that i had to have my key turned on to get the lights to work. On the new trailer with the keys on the lights still dont work, im wondering if i blew a fuse on the truck (havent tested the aux pin w/ key turned on). Does anyone know the number fuse im looking for?

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It only takes a few seconds to test all the fuses with a DVOM. It's usually a fraction of the time to look one up, lol.

And there are usually many fuses related to trailer wiring, so finding the one you need in the cryptic owner's manual fuse designations is a crap shoot.

There's something else that needs to be wired in the truck. I can't remember exactly what it is, but we had the exact same problem with my wife's Envoy. Everything on the horse trailer worked perfectly, except the interior light. When we had her brake controller installed, we asked the trailer place about our situation and they connected something in my wife's SUV. Works fine now.

On a 7 way plug only two wires are good to get 12vdc from and it depends on vehicle if it is constant with igniton on or off. Either the 12vdc charge line (red or black) or the aux (yellow).

I know that the 7.3 trucks use a relay under the hood for the 12v too. Not sure on the 6.0's though.

I know I have seen a few that didn't come with a tow package so they didn't have the relay installed.

Well i found that the aux. is only hot when the key is in the on position, i feel like an idiot but still wish it was constantly hot no matter what like the dodges. Now i have a problem with the integrated brake controller, it beeps trailer disconnected for a split second every time i hit the breaks. Anyone ever experienced that?

I had similar issues. The factory TBC's have known problems and many people have either replaced them with a new OEM unit or with an aftermarket one (like Tekonsha).