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Ask GM Tech (Cam) Your Own Question
GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29428
Experience:  GM Grand Master Technician 2007. 14 years experience.
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2005 GMC Sierra 3500: tail lights..turn signals and brake lights.

Customer Question

I have a 2005 GMC Sierra 3500 and my trailer plug does not have power to the tail lights. I have turn signals and brake lights. Is there a fuse that I can't find? I got stopped by a sheriff the other night and have not been able to find the problem.

Thanks,
Tony
Submitted: 6 years ago.
Category: GM
Expert:  GM Tech (Cam) replied 6 years ago.

Greetings and Welcome to Just answer.

There is a dedicated trailer brake light fuse in the underhood fuse block.

It has the label of TRLR PARK and is a 10 amp red fuse in front inner corner of the fuse block.

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GM Tech (Cam) and other GM Specialists are ready to help you
Customer: replied 6 years ago.
Cam,
Customer: replied 6 years ago.
Cam,
I replaced that fuse the other day and it did nothing. The lights are still out.
Expert:  GM Tech (Cam) replied 6 years ago.
Ok, do you have a test light? if so, go to the trailer plug and find a good ground. THen test for park lights in the trailer plug. The ground is the terminal at the 7:00 and the park lights are at the 11:00. See if there is power.. IF not, take the connector off the back of the trailer plug and look at it. See if there is corrosion. THe brown wire is the trailer park.
Customer: replied 6 years ago.
I checked the plug and there is no power for the lights. there is power to and through the fuse. all other lights working (turn, Flashers & brakes).
Expert:  GM Tech (Cam) replied 6 years ago.
So there is power on that pin to the trailer plug? if so, then that means the issue is in your trailer.
Customer: replied 6 years ago.
No, there is power to the turn signals, flashers and brake lights but not to the trailer tail and runnung lights. Could the problem be between the fuse and the plug?
Expert:  GM Tech (Cam) replied 6 years ago.
If the fuse I indicated is good and there is power to the 11:00 position on the plug, then it is not on the truck side. THe trailer usually does not have fuses in it, so the issue is likely the plug the plugs into the truck.
Customer: replied 6 years ago.
There is no power to the 11:00 pin. That is why I am confused. Fuse is good but no power to the 11:00 pin on the truck.
Expert:  GM Tech (Cam) replied 6 years ago.
OK, that clears it up. Find the connector on the back of the trailer plug and see if the brown wire has power.
Customer: replied 6 years ago.
Cam,

I pealed back the plastic cover over the wires up front of the back of the plug and found a 1 1/2" section of the brown wire that had been stripped and the wire was completely corroded. It must have been stripped when the truck was built as it was under the protective cover. Would that be something to talk to the dealer about with 65 k + miles on the truck?

Expert:  GM Tech (Cam) replied 6 years ago.
No, unfortunatly it is long past warranty so they cannot do anything. I would get a new plug and hard wire it in, much cheaper as they are about 30.