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aux 12v power to factory trailer plug

Discussion in 'Towing & Trailer Tech' started by lazypine, Apr 26, 2013.

  1. lazypine

    lazypine New Member

    Hi, New to this forumand i have a question to start. I have a 2008 Chevy 3500HD crew cab long bed single rear wheel Duramax with Allison with factory brake box and towing package. I tow an 18ft gooseneck horse trailer with living quarters that has a coach battery that is used for the breakaway source as well. I realized when my wife used the trailer for a long weekend that the truck was not charging the coach battery that I do not have 12v at the rear plug of the truck. Upon further investigation I read in the owners manual that there is a wire that needs to be connected in the engine compartment. There are two studs at the front of the fuse box in the engine compartment. One (closest to the engine) has a wire connected to it. the second stud(closest to the fender) is empty. Is there a wire hidden somewhere along the fender well that needs to be connected to that stud? Does anyone know what I'm talking about?
    Any reply would be greatly appreciated, thanks ,Neal
  2. Conlan Rose

    Conlan Rose Active Member 2 Years 1000 Posts

    Yes It should be in a wire bundle coming from the rear of the truck. Check under the brake booster, and around the fuse box.
  3. Jaele

    Jaele Rockstar 100 Posts

    hes Correct its a red cable, you will connect to the stud that is towards the outside of the fuse box, you will need a fuse and a nut.
  4. lazypine

    lazypine New Member

    Thanks for the quick response. The truck isnt here at the moment. Aren't the two studs already fused from inside the fuse box? I'm assuming the stud closest to the engine is powering the "in dash" break controller. Will be able to dig into this when I have the truck here. Thanks, Neal
  5. jake's silverado

    jake's silverado Epic Member 5+ Years 100 Posts

    Welcome to the forum!

    I just sent you a Personal Message. Reply with your email address and I will send you something to help.

    - - - Updated - - -

    Got your PM, email sent. Sorry for the delay...
  6. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    I don't know why Jake is being so secretive, but there should be two wires and two studs. The studs are different sizes and the hole in the wire connectors are different sizes (match the sizes and you won't scew up).

    One wire is for a 3rd party trailer brake controller and the other wire is for the charging system of the on-board battery.

    As @Jaele suggests, you will need fuses and nuts.
  7. jake's silverado

    jake's silverado Epic Member 5+ Years 100 Posts

    No secrets here Ray... Sometimes pictures help, with me anyway...when I had my first 2007 NBS it went back to the factory for noisy back seats and wen my neighbour ( he was quality control for NBS here in Oshawa) asked if there was anything else I mentioned the trailer wiring hook ups. They put together a PowerPoint with pictures and some instructions and gave it to me. I've asked a few times on how to post it here... but there always was some issue. I've sent it to a few folks here and would posted as everyone I send it to seems appreciative... So if you know how I can send it to you or I can see if I can do it now...
    Nope... to big ...
    Last edited: Apr 27, 2013
  8. Jaele

    Jaele Rockstar 100 Posts

    Ill send you my email and give it a shot.

    - - - Updated - - -

    Here is the walk-through
    If you are only looking at hooking up the 12v aux, skip to the last two photos.

    Thanks to [MENTION=25770]jake's silverado[/MENTION] for supplying this guide. I only uploaded and posted it

    Attached Files:

  9. RayVoy

    RayVoy Well-Known Member 2 Years 1000 Posts

    Nice info Jake, [MENTION=25770]jake's silverado[/MENTION], and @Jaele, thanks
  10. lazypine

    lazypine New Member

    I found the two wires, but the one between the fuse block and fender was marked 12v aux. when I hooked it to the stud I couldn't figure out where the wire went. I'm thinking that wire goes under the dash for an aftermarket brake box. I found the one under the master cylinder and hooked it up and Hooray! Power to the trailer plug. The only thing I don't like is that it's always hot. On my old truck I wired this line thru a continuous duty solonoid that was wired to a ign hot. That way my trailer, if being used, won't run the truck batteries dead when parked. Thanks for all of the great info, Neal

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