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12 Volt Trailer Batt supply


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Here is the deal. I installed the factory trailer brake wiring harness and added a trailer brake controller to my truck. That works fine. My problem is the 12 Volt supply from the plug to the trailer battery. I have used a test meter and there is no juice. I have posted this topic before and the replays directed me towards a 40 amp fuse in the underhood fuse box. Not it. There is not a missing fuse or blown fuse anywhere on this truck and I have yet to figure out where the trailer battery supply is. The manual or fuse legend does not help either. I tried to chase the wire back from the harness, but that is almost impossible. This wire should have been "hot" from the factory anyways. Somebody please help. I need that wire to run the interior lights on my enclosed trailer. I have been using it alot lately. Also it is about camping season, and it is sure nice to charge the trailer batteries while you are pulling it down the road. Oh yeah the dealership and techs here are clueless. They all say it should be hot.

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Here is the deal. I installed the factory trailer brake wiring harness and added a trailer brake controller to my truck. That works fine. My problem is the 12 Volt supply from the plug to the trailer battery. I have used a test meter and there is no juice. I have posted this topic before and the replays directed me towards a 40 amp fuse in the underhood fuse box. Not it. There is not a missing fuse or blown fuse anywhere on this truck and I have yet to figure out where the trailer battery supply is. The manual or fuse legend does not help either. I tried to chase the wire back from the harness, but that is almost impossible. This wire should have been "hot" from the factory anyways. Somebody please help. I need that wire to run the interior lights on my enclosed trailer. I have been using it alot lately. Also it is about camping season, and it is sure nice to charge the trailer batteries while you are pulling it down the road.  Oh yeah the dealership and techs here are clueless.  They all say it should be hot.

 

 

 

 

On my 2000 K3500 the fuse was missing AND the wire was not hooked up to the terminal on fuse block under hood either.

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Check the "STUD #2" maxi fuse in the electrical panel under the hood on the front fender. I think it is a 30 AMP green fuse. It was included with my under-dash wiring harness and it just needed to be installed.

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On the 96-99 models, both the blue 12ga wire for the brakes and the orange 12ga "hot" wire were included in the chassis wiring loom but were not hooked up at either end. You had to go fishing under the brake booster to find the ends. The orange wire for your 12V had a terminal attached to it that fit on either of the AUX A and B posts that are attached to the outside of the fuse block. The factory had 30A maxi-fuses already in the AUX A and B slots INSIDE the fuse box for these circuits. The wires were VERY difficult to find as there was not a lot of room under there and the factory taped them up until they were totally covered.

 

Another tough wire to uncover and find was the purple 18ga 3rd brake light that was taped up near the back of the truck. Again, the factory taped it up until it was invisible.

 

Good hunting!

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From the replies I am getting, it sounds like the wire is not landed. I don't recall seeing a "Stud #2" slot though. There is "Ignition #1 and #2". They are green, 40 Amp jumbo fuses (about 1/2 inch square and 2 inches deep). I have tested the wire at the plug and it is definately an open circuit. I just figured it needed a fuse some where. There is no place for a fuse. A reply on the other site also said, sometimes the fuse slot is covered by a plastic plug. This is very frustrating. It is almost worth just running a wire back to the plug itself, but I would rather use the factory wire if it is there. My 99 came with the wire "hot" from the factory, go figure.

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Well, you may want to run a wire anyway. Depending on how much current you want to run, and how bad you want to charge the battery. The wire that is stock is fairly small gauge considering the length it is run before it gets to the battery. I am not a electrical expert, but the voltage drop is fairly signifigant, and may be just enough to float charge your battery. If you are looking for real charging ability, I would upgrade that wire anyway. As far as Stud #2, it is in the underhood electrical center, running along the top of the box, should be about the fourth or fifth lug from the left. The OEM wiring harness for your brake controller should have a fuse taped in with it, along with directions for installing the fuse and the brake wiring. I think it is also listed in the manual.

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You did not say what vehicle you have, but I just installed a trailer brake controller as well. here is what i had to do:

 

install the factory supplied wire harness from the BEC (buss electrical center) in the driver side footwell. Taped into the factory supplied harness was a 40A fuse. I had to install the 40A fuse in the UHBEC (under-hood buss electrical center) in Stud #1. The trailer brake circuits are now HOT. Your trailer brake controller will not be active until a trailer (or trailer simulator) is hooked up to the receptacle.

 

Hope this helps...

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You did not say what vehicle you have, but I just installed a trailer brake controller as well.  here is what i had to do:

 

install the factory supplied wire harness from the BEC (buss electrical center) in the driver side footwell.  Taped into the factory supplied harness was a 40A fuse.  I had to install the 40A fuse in the UHBEC (under-hood buss electrical center) in Stud #1.  The trailer brake circuits are now HOT.  Your trailer brake controller will not be active until a trailer (or trailer simulator) is hooked up to the receptacle.

 

Hope this helps...

 

 

 

 

Truck description is in the sig. Trailer brake controller is hot. That is not the issue. I am talking about the 12 V supply to the trailer. There was no literature on the Fuse slot for this. There is none in the owner's manual either.

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You did not say what vehicle you have, but I just installed a trailer brake controller as well.  here is what i had to do:

 

install the factory supplied wire harness from the BEC (buss electrical center) in the driver side footwell.  Taped into the factory supplied harness was a 40A fuse.  I had to install the 40A fuse in the UHBEC (under-hood buss electrical center) in Stud #1.  The trailer brake circuits are now HOT.  Your trailer brake controller will not be active until a trailer (or trailer simulator) is hooked up to the receptacle.

 

Hope this helps...

 

 

 

 

Truck description is in the sig. Trailer brake controller is hot. That is not the issue. I am talking about the 12 V supply to the trailer. There was no literature on the Fuse slot for this. There is none in the owner's manual either.

 

 

 

 

I also have an 03, was looking for the fuse to make hot. Did a search and found out that the under the hood fuse box, upper left hand corner is a red plug, that is where the 30 amp fuse goes. Have not tried this yet, but mine does have a red plug in that place. Won't be messing with it till this weekend. Hope this helps and works.

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The biggest issue is that he has a Duramax. The Diesel trucks use stud 1 for engine control components, and the gas trucks use it for the trailer. I was under the impression, the trailer stuff got pushed to stud 2. It also looks like GM did not hook up the wire from the factory. So. it could be that wire issue as well. Good luck and let us know when you figure it out. You might also look in the back part of your manual. When I was flipping through looking for something else, I saw a multipage diagram shoing what each position in the underhood electric center did.

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I found it last night. The manual briefly describes it as Stud #2. It does not say anything about aux power to the trailer. Not it. As I was looking under Stud #2 for a disconnected wire, I noticed that Stud #1 had a dummy fuse in it. The reason I missed it was because the whole line of fuses came with a bar code sticker on them from the factory and they were all covered with part of a sticker or the glue from it. The other reason I missed it is that the dummy stud is red, like the 50 amp fuses. All of this BS for a red, sticker covered, dummy stud. Man I feel like a dummy. It was really very deceiving though. The only literature that I found on it was it could be Stud #2 and if it was blank it had a black plug in the hole. I did have to connect the wire underneath it also. The owners manual should have been more clear on this. When I traded in my 99, I robbed the trailer brake harness out of it to put in my 03 because in 03 it became an option. I know, they are supposed to be a different harness, nope. You just have to swap a pair of wires in the old harnes to match the new one(I bought a new one from the dealership and matched the pin out, then took it back for a refund). Anyways, I did not get a set of new instructions and a fuse. That sure came back to bite me in the a$$ in the long run. I have spent a little bit of time trying to solve this little fuse problem. Anyways, thanks for all of the quick, accurate responses.

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  • 3 weeks later...

So did putting a fuse in Stud #1 make the 12V terminal hot? I'm having the same problem with my 03 1500. I just put electric brakes on my trailer and need the 12V terminal to charge my trailer disconnect battery...all the manual says about Stud 1 is "don't install a fuse"

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So did putting a fuse in Stud #1 make the 12V terminal hot?  I'm having the same problem with my 03 1500.  I just put electric brakes on my trailer and need the 12V terminal to charge my trailer disconnect battery...all the manual says about Stud 1 is "don't install a fuse"

 

 

 

 

Yep, 40 amp (green) maxi-fuse installed in stud #1 gave me 12 Volts at the + terminal on the harness. Works fine.

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I need to add a brake controller to my truck before the first camping trip (which is about 2 weeks away), so all I need is the wiring harness from the dealer and I assuming I can use any aftermarket brake controller.

 

kinda stupid in this area, since I have never messed with brake contollers before.

 

Also if you don't have the brake controller installed, will the batteries on the trailer still be charged or will I have to do anything to get this to work? I do have the factory installed trailer plug on my truck. :P:lol:

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Depending on what brake controller you get, you may also be able to get a harness that plugs directly into your truck and the controller from the manufacturer of the controller..which was the case with my Prodigy. And then depending on your truck, you may need to install a fuse in Block #1 if you want it to charge your trailer batteries.

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