Question about 2003 GMC Sierra 1500

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No left brakr light on trailer when hooked up to truck on 2003 sierra

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If the brake light is working on the sierra, Check the right light in the left break socket. If that is good then. I would check continuity between the connection to the light on the trailer. Remember to always disconnect anything you are trying to check continuity or you may get a false reading. if that's good, check your power at the source where they first separate to go to there respective lights. Always trouble shoot from where you have power then go to next connection point. this should get the issue narrowed down.

Posted on Jun 25, 2009


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2 Answers

Right trailer turn signal does not work when hooked up to my 2003 gmc sierra. The light does work on the truck. Trailer light does work when hooked up with my other vehicles.

Check the plug at your gmc outlet, your right signal wire has been damaged before the plug somewhere. If you have a test light switch your right signal on and make sure it is working at the plug on your gmc, you will find it is not working, than trace the wire back from the plug till you find where it has been damaged or you can run a wire straight from plug to your right signal.

Jun 09, 2011 | 2003 GMC Sierra 1500

1 Answer

No power to the left brake light for the trailer plug but signal works fine on a 2003 gmc sierra

Look under the hood in the fuse pannel to the rear of the batterie.Think there is seperate fuses for the trailer in there.Lid will have diagram.

Jan 23, 2010 | 2003 GMC Sierra C/K3500

1 Answer

When I hook up to a trailer, the left turn signal and the left brake light won't work. I have tried several trailers with the same results. I own a 2003 gmc 3/4 ton pickup. I have two places to connect the...

it sounds like either the wires controling the left brake light and turn signal are borken or loose on your truck. or there could be a problem with the ground for the trailer hookup. you should take a volt meter and then have someone put the brake on and test at the hook on the truck side to see if you are getting any voltage there and do the same thing with the turn signal. if you do not have any voltage there you need to trace the wires back up into the truck to find where you do have voltage . you may find a broken wire as you go. How many wires are there in your trailer hook up?

Sep 22, 2009 | 2000 GMC Sierra

1 Answer

2003 chev...brake/signal/marker lights all work...but

Try turning on the parking lights on the car, while hooked up to the trailer, then test the lights inside... Typically, there is not a full hot wire going through to the trailer....

Sep 14, 2009 | 2003 GMC Sierra 1500

1 Answer

Replaced outlet,on car, for trailer, when hooked up, no lights on

sounds to me like your ground wire may not be conducting properly

Jul 10, 2009 | 2003 GMC Sierra 1500

3 Answers

I have a 2003 GMC 2500 HD. The left directional and left brake lights don't work on the trailer plug. The plug itself is not the problem and all lights on the truck work. HELP

Strange as it might seem, I had a similar problem with my 2003 Sierra 2500HD. All lights on the truck worked fine, and all lights on the trailer worked fine with the exception of the right brake light. I chased all the obvious possible reasons, (blown fuse, shorted wiring, etc). It turned out to be a sticky relay in the flasher unit in the dash. It is located behind the fuse panel on the left side of the dash, and is accessed through a hole behind the lower panel under the steering column. I removed the fuse panel cover and the lower plastic panel under the steering wheel and was able to remove the flasher unit. I ordered a new one but before I installed, it I checked the old one. The plastic cover comes off easily. There are two small relays for the trailer lights and the one for the right side was stuck in the off position. I freed it up, using a toothpick, gave it a spray of conatact cleaner and re-installed it. It is working fine now. I kept the new flasher unit as a spare in case the problem arises again.

Your problem may not be the same as mine, but at least you will know where the $100.00 flasher is located!

Hope this helps,


Jul 08, 2009 | 2003 GMC Sierra

1 Answer

Trailer brake controller problem

I found the problem. Talking with a technician from the controller company, we determined that it was a fuse problem. I found that the fuse to the CHMSL was blown.

Jun 30, 2009 | 2003 GMC Sierra 1500

1 Answer

05' Sierra 1500 trailer break lights

try This should help. Make sure the lights and trailer are grounded. Especially with a tilt trailer. The tilt pins carry the ground. Run a ground strap from the frame to the bed.

Jun 09, 2009 | 2003 GMC Sierra 1500

1 Answer

What is the capped off plug(blue) on right hand side of light harness on 2003 sierra used for. is this for fog light connection. there is not one on the left side.

The blue wire is to disengage disc brakes on your trailer. It is wired to your back up lights and has power only when you put it into REV

May 05, 2009 | 2003 GMC Sierra

1 Answer

No left brake light on trailer when hooked up to truck.

I had the same problem but when i tested the left turn signal then tested the brakes both brake lights would then work.

Feb 28, 2009 | 2003 GMC Sierra 1500

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