GM harness WTF?

**Tony** · 07-30-2009 09:20 PM

So I finally get to testing the stock trailer plug on my truck. The only thing that works is the ground, the constant hot(which should be the electric brake wire BLUE), and the left turn signal which also shows as hot when the brakes are applied. I used the "plug and play" brake controller harness, and even pulled the female trailer plug off the main harness to test.

Anyone have an explanation for this? 100%bone stock GM harness in an 03 Silverado HD. This may just be the icing on the cake that leads me to never buy another GM truck.....

**insanity** · 07-30-2009 09:26 PM

http://www.gm-trucks.com/forums/inde...howtopic=91681

I guess I was lucky the one on my new truck just worked. Owners manual have any info in it?

**phragle** · 07-30-2009 09:37 PM

why do you think they are bankrupt???

**BUIZILLA** · 07-30-2009 09:55 PM

did you forget to put the trailer relay in the engine compartment fuse box?

**Wobble** · 07-31-2009 04:10 PM

Originally Posted by Tony

So I finally get to testing the stock trailer plug on my truck. The only thing that works is the ground, the constant hot(which should be the electric brake wire BLUE), and the left turn signal which also shows as hot when the brakes are applied. I used the "plug and play" brake controller harness, and even pulled the female trailer plug off the main harness to test.

Anyone have an explanation for this? 100%bone stock GM harness in an 03 Silverado HD. This may just be the icing on the cake that leads me to never buy another GM truck.....

gm has separate fuses for trailer functions, located in left side of dash

**jwurl** · 07-31-2009 06:33 PM

You have to put a fuse in the fuse box under the hood...I work as a GM tech and have done tons of them with no problems. Most of the aftermarket trailer brake and light equiptment instructions are wrong and junk.. It is best to wire it with a test light... Jeff

**32storm** · 08-02-2009 09:04 PM

Originally Posted by Wobble

gm has separate fuses for trailer functions, located in left side of dash

Yes sir..I went nuts trying to back check for juice with my Simpson meter. Ended up just being a fuse on the trailer harness.

**32storm** · 08-02-2009 09:06 PM

Mine was on a 2500 GMC Sierra

**Airpacker** · 08-03-2009 08:10 AM

Also, somewhere in the infinite file that is Screw ups by the GM engineering forces, they decided to install a really useless JUNCTION BOX in the rear wiring harnesses. The front harness, rear light harness and trailer harness all plug into it. I have had to replace a few for non functional rear or trailer lights. Its mounted behind the tail gate, left side on the last box reinforcement. If its screwed and you can solder, just bypass it. The replacement one will fail later so just get rid of it now.

**Tony** · 08-03-2009 03:39 PM

It was missing a fuse under the hood, all of the underhood wiring is properly connected. I now have no power on the 12v constant pin, constant power on the ground pin, constant power on the tail light pin, no brakes, no right turn signal and a left turn signal that shows 12v when the brakes are applied.

**Tony** · 08-05-2009 11:48 AM

I pulled appart the harness plug thats up under the spare that has the color/function label for the trailer lights and checked all the voltage there.

Basically the problem is that whenever the running lights are on the electric brakes show 12v, and I have no right turn signal......this is getting very agrivating.

**Airpacker** · 08-05-2009 12:08 PM

unplug the junction box at the back and see if the correct wires have the correct voltages going into the box from the front to rear harness.

**Tony** · 08-05-2009 10:28 PM

Nothing on this piece of **** works. Anyone know the brake pedal/trigger wire color Im gonna hardwire the whole dammned thing.

**Tony** · 08-11-2009 08:04 AM

In the side of the dash on the right side near the center, There are 4 plug ins with a contact on the outside edges of each of the 4 plug ins like a relay would plug in there. Would this have anything to do with my problem?? If so what pugs in there?

The are labled.

10A 10A
[LT TRLR] [LT TRN]
ST/TRN

10A 10A
[RT TRLR] [RT TRN]
ST/TRN

**BUIZILLA** · 08-11-2009 08:07 AM

If it's to the right of the steering column and the left of the console itself that is the harness connector for a trailer brake controller, GM sells a plug-in harness to wire the brake controller in that area. Every new truck came with that harness adapter in the glove box with the owners manual

**Tony** · 08-11-2009 08:12 AM

No this is in the dash fuse pannel right inside the drivers side door. I have pics but their on a different computer. I already have the plug in pigtail that connects the brake controller to the pannel under the dash.

**erierunnin** · 08-11-2009 08:28 AM

I know how to fix it Tony!

http://sandiego.craigslist.org/ssd/cto/1315011305.html

**buck** · 08-19-2009 10:04 AM

Tony, sorry I just now saw this thread or I would have had you up and going in a couple of minutes. Looks like everyone pointed you in the right direction.

Next time call me at the shop. I'm here for ya.

Buck

**Tony** · 08-19-2009 10:05 PM

Late one night I was in the shop working on this and got so ****ed off, I thought to myself what would Buck do? So I went home and started drinking tequilla and watched some porn.

**buck** · 08-20-2009 09:14 AM

Originally Posted by Tony

Late one night I was in the shop working on this and got so ****ed off, I thought to myself what would Buck do? So I went home and started drinking tequilla and watched some porn.

I knew you'd do the right thing in the end.

Did you get the damn thing going or not?

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