Recently bought a 2024 Sierra Denali HD. It has a 120v outlet in the bed, but I have no power. I have tried several things, engine off, accessory mode and running. I even tried turning the bed/cargo lights on and nothing. Looked in the owner's manual and it states that the "DC/AC switch" must be turned on. Manual shows a button on the same bank as the exhaust brake, tailgate open, etc and there is no button there. Any help out there?