Trailer Harness Power?

masonbid · February 11, 2009

I recently bought a 2006 Sierra. When I went to check for power at the trailer harness, there was none. I went to look under the hood for a wire that may be disconnected but I was unable to find any.

In the trailblazer there is a red wire that just hangs there until you want to bolt it onto the aux power pin under the hood.

Does anyone know if there is something like the trailblazer or am I missing something?

Outbacker · February 11, 2009

I lost power to my 7 pin connector once, and it turned out to be a loose ground wire back at the connector. I tightened it up and it was good to go. There may also be a in-line fuse somewhere that may have blown, so you may want to have a boo for that as well. Good luck.

fieroaddiction · February 11, 2009

The wires you need to connect are inside the underhood electrical center. You can't get to the wires by just removing the top access cover, you need to remove the fender brace and then take the whole cover off the fuse block. There should be two red wires with ring terminals and a stud to put them on. You need to add a fuse to put power to the stud. There's also two blue wires that plug together. One is power for the plug and the other is power for the brake controller. I'll see if I can post the details from the service manual.

masonbid · February 11, 2009

Thanks for the help. I will check tomorrow after work. I already took a quick look today, but I guess I need to remove more parts.

97SierraGMC · February 11, 2009

you dont need to remove all of that....

you can usually get a hold of the ring on the end and just pull its only wrapped up in a little bit of electrical tape... it just pulls right out and you can throw it on the stud.. at least that is how it is on the gmt-900s i cant think of how a gmt-800 is right now...

sonjaab · February 11, 2009

The GMT-800s don't need anything to be hooked up !!!!!!!!!!!!!!!!!!!!

ONLY the gmt-900s need the 2 loose wires hooked up to the underhood

fuse center.

Either you are checking the wrong power lug or using a pre-03 trailer plug in!

GM changed the pin out arrangement after 03..................

You must add a maxi-fuse to either stud 1 or 2 (can't remember) to power up the

trailer power wire as GM quit installing it from the factory.

I went thru this hassle trying to wire up my 01 compared to my 04 untill somebody

in the know clued me in !!!!!!!!!!!!!!...........geo

fieroaddiction · February 11, 2009

The GMT-800s don't need anything to be hooked up !!!!!!!!!!!!!!!!!!!!
ONLY the gmt-900s need the 2 loose wires hooked up to the underhood

fuse center.

That's not true!!!!

The following pictures are from a GMT800 2003. This truck was factory equipped with a trailering hitch and 7-way connector, but the underhood wires were not connected and the fuse not installed. Some trucks are connected at the factory/dealer and others are not.

This is what you will most likely find when you pull the cover off of the underhood electrical center. Two red wires with ring terminals and two blue wires with inline connectors.

This is how they should look if you want to power up the trailer and brake controller plugs... The red wire leading into the cab powers the trailer brake controller harness and goes on stud 2. The red wire leading to the chassis harness powers the trailer connector and gets connected to stud 1. The blue wires get connected together.

You also need to install the proper fuses. On this particular truck the 30A Stud 2 fuse was already there and there was a dummy fuse in the stud 1 location.

STUD 1 Fuse

40A

Trailer Wiring, Automatic Level Control (ALC) Compressor Relay

STUD 2 Fuse

30A

Trailer Wiring, Emergency Vehicle Roof Lamp Relay

The in-cab wiring for the trailer brake controller was changed in '03, but that does not affect the B+ power to the trailer connector.

fieroaddiction · February 11, 2009

you dont need to remove all of that....

On a GMT 800 you can probably get in there enough to see if they are connected without removing anything, but I think you'd have a hard time connecting them without removing the cover. It's just four bolts to remove the fender brace and the cover pops right off.

masonbid · February 11, 2009

Jeeze another 4 hours until I get home. I guess I will find out later

tick tock tick tock

masonbid · February 12, 2009

Ok, I took a look under the hood. The fuse wasnt blown to stud 2 and the wires were all connected under there.

It was too cold out to do anything involving me laying on the ground so Im not sure if the connector is loose or has a bad ground somewhere.

sonjaab · February 12, 2009

SORRY.......I again forgot I had to be more LITERAL when I post here:

IF YOUR GMT-800 TRUCK DOES HAVE THE FACTORY INSTALLED TRAILER TOW PKG.

AND PLUG YOU WILL not HAVE TO HOOK UP ANY WIRES TO THE UNDERHOOD FUSE

CENTER.........................

I had TWO gmt-800s with factory tow pkgs. and neither required hooking up any

loose underhood wires that needed to be connected to power up the rear FACTORY

plug. BUT the pin-out arrangements were different and the 04 required that a maxi-

fuse be installed in either plug 1 or 2 (forgot which) to power up the aux. trailer power

lug......................

masonbid · February 12, 2009

I talked to the previous owner and he said that his snowmobile trailer worked just fine as PnP. Stud one has a blank fuse and stud 2 has the 30amp fuse.

The only other thing i can think of now is either a wire got pinched(unlikely) or the connector is loose/bad ground.

sonjaab · February 13, 2009

MASON.......Swap the maxi fuse into stud 1 and see if it powers up the

power lug in the plug.........................

OmarR · February 13, 2009

Stud one has a blank fuse

That's your issue. Just pull out that red plastic piece and install the proper 40 amp fuse. You will then have 12V at the trailer.

Rat4go · February 13, 2009

Stud one has a blank fuse

That's your issue. Just pull out that red plastic piece and install the proper 40 amp fuse. You will then have 12V at the trailer.

+1. Just did this on my bro in law's 2004, and I'm about 99% sure it's all I needed to do on my 2003, but that was 6 years ago!!

As was also mentioned, you can easily swipe the fuse from something else to put in place of the plug to confirm that you get power back there as a quick double check.