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Discussion Starter #1
i have a 05 lly, problem is i have no 12 volt power to my trailer when i hook up my trailer lights , So when i'm driving its not charging my battery on my trailer
What do i need to do :help:
 

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GM doesn't put a fuse in the fuse box for your 12 volt power to the trailer. Lift your hood; pop the top on the under hood fuse box and standing by the fender upper left corner you will see a red colored plastic plug. Take that out and put a 40 amp fuse in. You will now have power to the trailer.
Cheers,
AussieDMAX
 

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Discussion Starter #3
Thanks for the help
 

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GM doesn't put a fuse in the fuse box for your 12 volt power to the trailer. Lift your hood; pop the top on the under hood fuse box and standing by the fender upper left corner you will see a red colored plastic plug. Take that out and put a 40 amp fuse in. You will now have power to the trailer.
Cheers,
AussieDMAX
My '06 Sierra owners manuel says specifically NOT to install any fuse in place of that plug.
 

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If it is just for an 06 Sierra, it probably is stating for a gas engine. With the duramax it is ok. You won't get power to your trailer otherwise.
 

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My truck came with a trailer brake controller harness and also a 40amp fuse.
 

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If it is just for an 06 Sierra, it probably is stating for a gas engine. With the duramax it is ok. You won't get power to your trailer otherwise.
The manual only refers to the location as "stud#1". If a 40 amp fuse is installed, any idea what "pin" location it would be on the truck end of the 7-way trailer plug?
 

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On the truck its the pin just to the left of the top center notch.. 11 o'clock you could call it as you look at the end on the truck from the back of the truck :)
 

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actually, scratch that, I was looking at the diagram for a trailer end adapter. It'd be just to the right of the notch, in the 1 o'clock position.
 

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Yes, it would be the pin labeled + on your cover of the plug. Just like G-reg stated the 1 o'clock position. If the fuse isn't installed, you won't charge the battery(s) on your camper or have interior lights in your trailer. That pin is hot all the time....The interior lights on the trailer I haul turn on even with the truck off.

Rcher: That 40 amp fuse is for stud #1.
 

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Went outside with a circuit tester today, no power to that terminal (at the hitch plug). I am going to go get the fuse this wekend & see what happens.

Thanks guys.
 

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If I'm not mistaken the truck has to be running. Make sure you test it with the truck running.
 

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If I'm not mistaken the truck has to be running. Make sure you test it with the truck running.
nope, truck needs not be running to be powered at the pos terminal on the trailer plug...
It does as stated before have to have the fuse in the Stud#1 spot though..
once the fuse is in there you will have power at the plug...
good luck!!

:grd: :exactly:
 

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How big is the wire to the truck plug. It must be pretty hefty to take 40 amps.....
 

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I dont know the exact size but it isnt as big as you would think. If you have any serious 12V needs on the trailer it isnt adequate, but for 99.5% of the people its fine.
Because the circuit is constantly hot I wired mine into an ignition triggered relay so that it would only provide power when the truck was on. We often stop for 6-8 hrs to sleep while on the road. If I have to run my furnace I didnt want my truck batteries equalizing as the trailer battery drains down. I got tired of disconnecting the plug from the back of the truck to protect my truck batteries ( I figured one of these times I would forget to plug it back in )
If anyone is interested in wiring theirs like this send me a PM and I will fill you in. Its really quite simple to do.

Scott
 

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Do the isolation relay( or isolator),
You will forget and run down the truck batteries....!!!!!!!!

You can remove the wire from the stud, add a relay
and a wire from the relay to the stud...
 

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Essentially thats all there is to it.

Get a standard 40a relay (commonly used for auxiliary lighting) any good auto supply will have one.

This all takes place in the underhood electric center, remove the bracket (4- 14mm screws) and then pull the cover off, it has tabs that lock it down.

find the stud for post #1, take the ring terminal off and cut it and connect it to the #30 terminal on the relay. I usually put the in the open area towards the rear on the electrical box, rear of the panel.

connect #87 to the wire you just took off (this is the wire that goes to the trailer feed)

connect #86 to a good ground ( there is a screw under the panel that goes into the left fender to hold the base of the electrical center, you can tilt the panel and access it for a ground, I ususally put a star washer on it to get a good bite on the ring terminal)

using an ATM fuse tap I pulled a signal form the fuse marked "IGN E" its a 10a fuse and is only on whent he ignition is on.

tidy up all the wires and make sure nothing is pinched, check the plug for power before putting everything back, you should only have power to the trailer plug "12V +" when the truck is running now.

you will need :

40a relay
4 female spade terminals
2 ring terminals
approx 18" of 14ga wire
a few zip ties for tidying up your work
star washer for ground 5/16 size


sorry I dont have any pics of this, if anything is unclear feel free to PM me.

good luck...

Scott
 

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sweet, thanks bigdisneydaddy!
 

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The ATM fuse tap goes to #85 on the relay. I think I forgot to say that earlier.
 

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THANK YOU Gentleman!!!!!!!

I would have never (or sometime from now) realized I did not have 12v power going back to the trailer until I read this thread. GM even gave me the 40amp fuse, da.

I'm thinking I overlooked it when I installed my prodigy, I bought the pre-made harness from tekonsha that goes from the fuse box to the brake controller. SO I put the GM harness in my toolbox without even taking it apart, figured that i didn't need it. For whatever reason I looked at it the other day & realized the 40amp fuse was taped to the harness. But even still it was'nt clear where to install it.

THanks again.
 
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