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.