View Full Version : 12 Volt Aux feed on 7-Pin Trailering Connector
Can anyone tell me why the aux 12 volt feed on the trailer connector isn't hot ? I have a 2003 GMC with the trailering package. The book indicates that lug #2 should power it and it has a fuse. What am I missing ? :(
On my 2001 I had to install the fuse, it was in the jockey box with the brake accuator wire harness.
[ 11-10-2002: Message edited by: chipper ]</p>
Jackmchome
11-10-2002, 22:16
The 40 amp fuse in the glove box goes into the underhood fuse center in the top, left, position. This will hot up the 12v feed.
FisHn2DMax
11-10-2002, 22:28
Be CAREFUL!
We all got a surprise on the 03's when attempting to wire the brake controllers. It appears GM decided to change the pin-out on the Brake controller connector from previous years to be compatible with a new ISO wiring standard. My 03 Manual was wrong! When I wired mine, I had to swap two wires on the controller harness to make it work properly. As I recall, my trailer controller would apply trailer brakes if the lights where on. I had to find the real 12V line and swap it around. There are threads on this site that go into much detail on this. I had to learn the hard way. Not one of GM's best ideas! Worse, they didn't inform the customer and cheated the 03 customers by not suppling a brake controller harness and with no documentation leaving most us to find out the hard way!
An Easy way to tell is to turn on your lights, if you now get the 12V your looking for, you've got to change the two wires around. Also, make sure your trailering fuse is in the box and is good!
Good Luck!
:D
AbqGeorge
11-11-2002, 00:02
Not having that harness come with my 2003 caused me three hours time and ran off about 40 break-in miles tracking it down (that was the good news).
The dealers are totally unprepared to supply this part. Two out of three dealers in Albuquerque did not have it. And this was after nearly 30 minutes at each one toe tapping while they tried to find the part number. Finally tracked it down. Cost me $36 !!! I'm requesting a refund from Chevy since page 4-90 of the owner's manual clearly states that the harness is included.
BTW, the part number is:
15085418
It's called the "Z82 - Glove Box Jumper"
Sorry, I must not have been very clear (and I sure don't know how I got 2 posts since I was in bed before 11:00 PM) in my original question - it's the rear 7-pin plug that does not have a "hot" 12V pin. This has nothing to do with the electric brake controller surprise that GM gave us. The book is unclear.
chevmeister
11-11-2002, 22:12
In responce to your question. On my 02 there was a fuse in the bag with the brake controler. I had to install it in one of the open spots in the engine compartment fuse box. Dont want to say which spot due to the fact gm might have changed that too, (plus I cant remember) . But I believe it was a 40 amp fuse.
Raptorrider2001
11-11-2002, 22:44
I also noticed yesterday that mine does not seem to be charging my trailer battery. I did not install the fuse because I did not know what it was for or where to put it. I could certainly use some help getting it going. Thanks ;)
Maverick
11-12-2002, 01:37
Rap-master,
You..you..you got to install the fuse. Thats the best I can rap. The 40amp fuse did install in the top left slot of the drivers side under hood fuse panel. This should allow your batteries to charge and get 12 volts back there at the plug for Snowmo man..man..man. There I go rapping again. :rolleyes:
I should say that this is for trucks with a factory installed trailering package. If it still doesn't work after doing the above....send me an email and I can tell you what you need to do next.
[ 11-12-2002: Message edited by: Maverick ]</p>
FisHn2DMax
11-12-2002, 01:58
Sorry SnowMo,
Your were clear, I just jumped ahead and assumed you were refering to the Brake controller problem that drove most of us 03 owners totally nuts.
I too had the problem of no 12V Aux power at the rear bumper factory 7 pin when hooking up to a trailer to charge it's weak batteries. I discovered that the 40 amp fuse was missing in the fuse box? And It wasn't in the glove box! I dropped by the GMC dealer and they put one in while I waited. On the 03's, the dealer should have installed the 40 amp fuse during the pre-delivery inspection phase if you have the trailering package option. IMHO, GM really messed up on this whole trailering wiring change in 03! Even the dealers had no clue that GM had changed the wiring, and they just stopped sending the controller harness and 40 amp fuse in the trucks. They required the dealer to now install the fuse, since the factory didn't supply it. The problem is, GM never told the dealers put the fuses in.
"GM owes all 03 owners a 40 amp fuse, an updated brake controller cable, and an updated trailering wiring diagram addendum for the 03 owners manual".
Look in your Engine compartment fuse box and verify you have the 40 amp trailering fuse, if not get one or go to your dealer, if you do, make sure it's good and installed in the proper location. Once you get a working fuse in this location your 12 volt Aux. problem should be solved.
Good Luck! ;)
Raptorrider2001
11-13-2002, 20:11
Stopped by the dealer yesterday after reading this post. The fuse came with the wiring harness so I took it to the service writer and asded him about it. he did not have a clue as to what I was talking about. I showed him page 4-94 in the owner's maual but he still could not figure out where to install it. After talking to 2 other writers, one took the time to look it up and went out and installed it. All the while they were talking and looking things up, I kept looking at all the certificates on the wall showing all of the schooling and training they had received. Couldn't help but chuckle. To give credit where credit is due, at least one took the time to try and look it up. From now on, I will at least ask for him. I'm just glad that in my 13000 miles, I have not had to take it in except to get the trans. codes updated and the steering wheel sqeak and moan they could not find. :confused:
stutzismydog
11-13-2002, 22:19
FisHn2DMax~
I have a 03 Dmax with the (trailer wiring package) at least that is what I paid for when I purchased the Truck. I did not receive the brake controller connector with my 03 truck, so I removed the Prodigy brake controller and connector from my 01 truck that I was trading in. Well you have herd all of the horror stories about brakes on the trailer being activated when the head lights are turned on, mine was while in a tunnel and the auto head lights came on and you can just guess what happened next.
My question to you and others is
FisHn2DMax
11-14-2002, 01:47
STUTZISMYDOG~,
If you've already got your prodigy working,( after much trial and error, no thanks to GM LOL,,) and your electric brakes on your trailer are working, your fuse is already installed! You should already have the +12 v Aux power on your 7 pin connector plug since this comes from the same 12 volt source as the brake controller uses to power your electric brakes. It sounds like your all set!
As for where the fuse is, I'll post a picture to show you where the fuse is in the next few days. A picture in this case is worth a thousand words!
Keep in mind, Not all travel trailers are factory wired for tow vehicle charging. I had to add the charge wiring for my 5'er trailer. If you do this, make sure you disconnect the trailer harness from the tow vehicle when camping or when using the trailer, or you could drain your trucks battery(s)!!!!! A battery isolater can be easily installed on your trucks battery ( 12V accessory battery for diesels) to prevent this from happening.
:D
stutzismydog
11-14-2002, 10:52
Fishn2Dmax~
Thank you for your response. I just checked my + 12 v AUX power pin and there is no voltage and I also checked the trailer brake pin and there is 12 volts. As I stated before the brake controller connector is from a 01 Silverado that had the 2 wires reversed by a service tech. and every thing seams to work THIS TIME, but the 12v AUX power pin. I found this in another thread:
BY AbqGeorge:
Thanks to FisHn2DMax I too put in a fuse in place of the B+ plug (guess the "plug" part should have triggered a thought) I now have power to the 7 pin connector - it is shown as Lug#1 (upper left corner). I believe the fuse that corresponds to the elec brake controller is Lug#2 (upper right corner). That fuse was already in place which is why the brake controller worked fine. Until I discovered I had no aux lights inside my trailer I was unaware that I was not getting a 12 volt feed to the trailer. My only remaining question was a 30 or 40 amp fuse. Lug #2 is 40 amp so I went with a 40 on lug #1.
stutzismydog
11-14-2002, 17:58
Snowmo~
Just to give credit where credit is due
Raptorrider2001
11-14-2002, 21:25
I have an 02 and am running the Prodigy controller but did not have power to the trailer. I had to install the fuse. It goes in the top left corner or the fuse panel as you are looking at the box from the side of the truck. If you turn the lid over, it will show a place for 2-40 amp fuses and there is only one installed and the first one is open for a fuse.
The entire fuse block in the 2003 has been changed to take the new style fuses. The old style fuse will not work. The harness that used to be included in the glove box is available on several trailer hitch suppliers web sites for around 10 dollars. The part number for the 2003 harness differs from the 2001 + 2002 number, but I have been unable to find what the difference is.
The old harness had a brown wire which was used to lightup an iluminated brake controller when the headlights were turned on. It could be that this wire was switched with the brake light wire, causing the brakes to come on with the lights.
Joe
imported_
11-15-2002, 10:00
Southwestwheel.com has a very nice "plug and play" harness for the '03 for about $20, shipped.
Since I feel that GM screwed me out of it I chose the aftermarket route over the more expensive GM part. Plus, it got delivered right to my door in a few days saving me a drive to the stealer.
The brown plug plugs into the second socket from the left on the top row of fuse box located on the interior firewall above where the clutch pedal would be. There is a long plastic nut holding the cover on which can be hand loosened.
The other end plugs into your controller. I just towed about 500 miles on mountain roads and it worked just fine.
It goes w/o saying that the Duramax is a towing beast born and bred to tow and to stop on steep mountain roads.
Husker Fan
11-15-2002, 10:45
Ok, now I
Ranger354
11-15-2002, 11:00
Somebody mentioned above that on the 03s the trailer brakes would come on when they turned thier lights on.
This happens on my 02. Just thought it was the brake control itself. This has been driving me crazy thinking that I have hooked it up wrong when I know it is right.
Can anyone point me to which thread detailed this stuff. Please.
As for unhooking the 7 wire trailer connector to your trailer when NOT in use, or risk draining your battery.
This 12V line that we are talking about SHOULD be on a relay, and only juice the line when ignition is started.
With all the confusion about all this, HOW hard would it have been for the factory to INSTALL this fuse? What would it benefit to have it NOT hooked up?
As far as brake controllers go...
Why cant the factories install a FACTORY brake controller? One that senses the pressure being applied to the brake calipers. And also senses decelleration. They got computers to do everything else in these trucks, why not a smart brake controller?
People buy these trucks to TOW. A trailering package SHOULD contain everyting BUT a hitch!
SoCalDMAX
11-15-2002, 14:24
Tom, I see why you own your own business.
You are FAR FAR too logical to make it in the corporate world. ;)
Regards, Steve
Onebigcanuck
11-15-2002, 15:39
I called the Manufacture of my brake controller & he advised me that on the 2003 the brake light wire in the underhood box had been moved by GM from the upper right to the lower left. I took my harness from my 2001 and moved the light blue wire (vehical stop lamp switch to brake controller input)(Upper right) and placed it in the position of the Brown wire (brake controller illunition) (lower left). Works like it is supposed to.
On the Aux power for the 7 wire connecter, this is the upper left not used comm (1 ?) in the under hood fuse block.
Mine had a Red plastic plug marked B+. Also works no problem
I checked 03' GMC 3500 CC w/trailer option today and it does have the 40 amp( I think that is what it is) fuse installed. Do not know if factory or dealer installed it? It was built at the Flint plant. As per previous post the center power tab in the trailer plug connector is not hot when the ignition is off. I tested w/VOM w/ignition off, and had no power. Will try w/ ignition on and hopefully it will be hot.
Husker Fan
11-16-2002, 19:27
I called my dealer because my trailer brakes work fine, but I don
Powered by vBulletin® Version 4.2.5 Copyright © 2025 vBulletin Solutions Inc. All rights reserved.