Hello guys, I own a 2007 GMC Sierra Z71. Really happy with the truck, but having a problem with my trailer running lights. Recently changed out my lights on my boat trailer; all works well(both blinkers, brake, and flashers) but no running lights. Had a buddy yesterday back up to my trailer with his truck, and running lights work, so it's not the trailer. Running lights on my truck work(not sure about daytime running lights) Looked in the fusebox under the hood, and checked fuse for running lights. Fine...is there a relay I should check? Any help is appreciated! Thanks, David Cutrer

 

Those may be running in a series circuit. So if one bulb burns out, the rest dont get power. So check the bulbs.

 

I think the bulbs are connected in the series of the circuit. You need to check the circuit. I am sure you will be overcome with the problem.

 

check your connection on your truck to the trailer, your running lights on your
truck may work but you may not have power to the connector on the truck side. Are you using the factory 7 pin harness? check to see if you have power, if not you may have a broken wire usally in the connector its self.