The factory installed trailering plugs are reversed in location per the operating manual. The problem was experienced the first time I attempted to pull my boat. 200-500 miles on my 2021 2500HD. Neither plug will power the lights via the 4 pin or the 7 pin. Voltage check on each pin in each plug reveals voltage only on one pin. I have the fifth wheel gooseneck trailering package which states the 4 pin and 7 pin plug are on the bumper and the 7 pin and camera port plug is in the bed behind the left rear wheel. The operating manual clearly shows the location with two photos. The dealer is bound and determined that these are the correct locations despite what is in the manual. I have suggested to them to reverse the mounted plugs to the manual depicted location. Under the bed the mounted plugs are plugged into a wiring harness plug at each location. They want to open the wiring harness and look for a bad wire. The dealership will not listen. To me it is a simple switch the plugs and see if it works. 30 minute job on the lift with no intrusion into the wiring harness. If this does not resolve then dig deeper.