2000 GMC Sierra Trailer wiring

sheepofblue · 01-27-2005, 11:36 PM

OK so I have a six wire and need to go seven to the new trailer. I have a brake controller plug under the dash and a six wire harness to the back. Is it possible to replace the 6 wire with a 7 wire from the dealer or is this a major mistake to even think about?

Thanks

SomeStrangeGuy · 01-28-2005, 12:56 AM

edit: nevermind.

what kind of trailer is it? does it have interior utilities that require the 7th wire or is that just how it came?

edit2: Click Me if you don't mind a trip to walmart. actually link is weird, reference part ## R74645

sheepofblue · 01-28-2005, 1:15 AM

Quote:

Originally Posted by SomeStrangeGuy

edit: nevermind.

what kind of trailer is it? does it have interior utilities that require the 7th wire or is that just how it came?

edit2: Click Me if you don't mind a trip to walmart. actually link is weird, reference part ## R74645

The trailer comes with 7 wires, I will know more when I look at the docs and get the meter out etc. So I would need a 6 to 7 (not seen one yet). However I think the seventh wire is for charging the brake battery and maybe lights. The truck comes stock with a 6 wire harness to the back however there is an option of 7. I thought there is a chance that it is wired and I just need to get the other harness from GMC.

Anyway I am figuring it out and thought a site member might have a similar setup since Chevy's and GMCs (after 2000 I think) are the same setup and lots of folks probably have trailers for bikes or camping here

G-Force Junkie · 01-28-2005, 2:18 AM

6 wire to the back??? I'm not familiar with GMC wiring...usualy vehicles have a standarf 4 prong, or the 7 prong. The 7 prong just adds a 12v for battery charging (8-10 gauge black), a blue for trailer brakes, and a orange for backup lights. If you already got brake controller harness in the cab, it usualy has 4 wires.

G-Force Junkie · 01-28-2005, 2:21 AM

Check this out http://www.etrailer.com/faq/wiring.asp
sounds like you need to run a 12v wire fronthe battery to the rear of your truck. There are wiring diagrams for this on the 'net, I'll see if I can find it. Use a 8 or 10 ga wire.

G-Force Junkie · 01-28-2005, 2:24 AM

...actualy, it appears the 6 wire would work, its only missing the auxlurity wire...what is typicaly used for back up lights. But considering 99% of trailers (unless we are talking boat trailers) with electric brakes have 7 pin, I would convert yours. It should only take rewiring at the bumper and tapping into the reverse lights wire.

SomeStrangeGuy · 01-28-2005, 3:28 AM

Quote:

Originally Posted by sheepofblue

So I would need a 6 to 7 (not seen one yet). However I think the seventh wire is for charging the brake battery and maybe lights.

did you click the link above?

HondaGalToo · 01-28-2005, 6:01 AM

Congrats on the trailer. Can't help ya with the wiring, the trailer place installed mine since I only had 4 pin, and did the brake controller too. I've only seen 4 and 7 pin. 6, huh. Good luck with it!

sheepofblue · 01-28-2005, 9:07 AM

I looked and while mine is a six and I have 6 in the harness I only use 4 right now. Looks like it is time to string wire

Etrailer also had info on my truck specific but I was hoping to swap a harness rather than string wire for slickness of install

SomeStrangeGuy · 01-28-2005, 10:14 PM

Quote:

Originally Posted by sheepofblue

I looked and while mine is a six and I have 6 in the harness I only use 4 right now. Looks like it is time to string wire

Etrailer also had info on my truck specific but I was hoping to swap a harness rather than string wire for slickness of install

what the hell am I missing?? I've done just about anything you can do electrically to a car and I'm still confused

. Can you draw a diagram

sheepofblue · 01-28-2005, 10:30 PM

Quote:

Originally Posted by SomeStrangeGuy

what the hell am I missing?? I've done just about anything you can do electrically to a car and I'm still confused

. Can you draw a diagram

It is confusing. 2000 GMCs came two ways, with tow package and w/o
The 'with' is a 7 pole connector wired complete just plug a brake controller in and go.
The without (aka mine) has wiring exposed above the spare tire with 6 wires although i have found out 2 of the 6 are for weird things. This is easily connected to a 4 pole system. Also the truck is wired to accept a controller in the cab. What I wanted was to get the OEM 'with' wiring harness and plug it into my truck. Thus I would have a poor man's tow package (I already have the hitch reciever). However I have been told by the dealer that although the cab is wired for a brake controller the existing wiring is not able to have the HD tow package harness added. I am going to look at my truck an the Helm's Manual a bit more but figure I will have to drag some wire to the back from the fuse box.

SomeStrangeGuy · 01-28-2005, 11:31 PM

Quote:

Originally Posted by sheepofblue

It is confusing....I am going to look at my truck an the Helm's Manual a bit more but figure I will have to drag some wire to the back from the fuse box.

I gotcha now I think, and I think you may be missing the fuses and terminals that the HD has. But yeah you're on the right track, as the primary diff between 6/7 wires is that the 7 has an extra 'power' wire to run onboard aux. equipment. From what I can recall this is usually rated no less then 20a.

BillAce may have more experience with this then I, but then again the question is not a complex orchestration of thiele-small params. rather simple 12vdc with current limiting.

Did I ask what kind of trailer yet?

...and in the end I highly recommend sourcing an all out re-kit rather the just adding some conductors to the existing. Just cleaner and neater, and since the labor is the same price

sheepofblue · 01-28-2005, 11:42 PM

Quote:

Originally Posted by SomeStrangeGuy

I gotcha now I think, and I think you may be missing the fuses and terminals that the HD has. But yeah you're on the right track, as the primary diff between 6/7 wires is that the 7 has an extra 'power' wire to run onboard aux. equipment. From what I can recall this is usually rated no less then 20a.

BillAce may have more experience with this then I, but then again the question is not a complex orchestration of thiele-small params. rather simple 12vdc with current limiting.

Did I ask what kind of trailer yet?

...and in the end I highly recommend sourcing an all out re-kit rather the just adding some conductors to the existing. Just cleaner and neater, and since the labor is the same price

That is why I wanted the whole harness, about $90 but it would have been cleaner and more reliable. I have a link at etrailer.com with instructions but it is not as clean.

The trailer is a Shadowmaster and if the ice storm doesn't screw the roads over to bad I will have pics tommorow

sheepofblue · 02-27-2005, 12:19 AM

Update: My harness came in. Not only will it hook into the existing wiring and fuse box it comes with some fairly detailed instructions. Anyone that is looking to wire up a GMC/Chevy from 2000 up should consider this route.

abtech · 02-27-2005, 1:56 PM

Quote:

Originally Posted by G-Force Junkie

...actualy, it appears the 6 wire would work, its only missing the auxlurity wire...what is typicaly used for back up lights. But considering 99% of trailers (unless we are talking boat trailers) with electric brakes have 7 pin, I would convert yours. It should only take rewiring at the bumper and tapping into the reverse lights wire.

The aux wire is also used for interior lights on enclosed trailers.