Trailer Light Issue

Logan Lanfear · August 26, 2020

Hey guys,

My 2000 GMC Sierra has had an issue since I purchased it. While towing, the left side trailer light does not work. I had previously chocked this up to a trailer with a bad light but I recently replaced the lights on a new to me utility trailer. This "new" trailer had the same issue with no left side marker light, brake light or blinker. I have checked the fuses as well as changing the bulbs around on the trailer. I have confirmed with another vehicle that the lights work correctly on the trailer. Yet when I plug my truck in, I only have the right side lights. The right side is bright and working well. My truck has the factory tow package with the 7 pin round style plug. I have taken the plug apart and found no corrosion. Im not sure if a wire got crossed somewhere or if there is a light issue on the truck. Any help or spots to check would be appreciated. I will double check my fuses and make sure that they are all functional.

diyer2 · August 26, 2020

Look under the rear bumper. Check wiring harness.

Have you checked the plug with a test light?

Logan Lanfear · August 27, 2020

No visible problems with the harness or the plug. Also no power at the plug tested with multiple trailers as well as a multimeter. Also update: I have no brake lights at all just right side blinker and running light.

rjgti · August 27, 2020

i think that there is a junction box above your spare tire for the rear harness, have a look there

Logan Lanfear · August 28, 2020

Checked the harness, no problems there either. I'm not the first person to be in here searching for the problem. Honestly, i've been looking for a reason to upgrade and this might be it. Either that or im tapping into the taillight harness just to get me by.

Edit:

Got it figured out, turned out to be a burnt wire in the trailer harness. Im guessing it was due to a bad ground. I cleaned the grounds and fixed the wires. Hopefully it doesnt repeat.

Edited August 31, 2020 by Logan Lanfear

ChevroletTough · August 31, 2020

I had similar problems, I ended up replacing the 7 pin connector. It should disconnect from the harness going in, buy a new one and replace. Easy swap out.