This may have been brought up sometime in the past but its new to me and I thought I would pass it along. Did you know that Chevrolet and GMC trucks have separate fused circuits for trailer connectors? My running lights worked fine on our 2006 Chevy truck but wouldn't work on the trailer, I tracked it down to a blown fuse under the hood that is just for the trailer, at the same time I found another blown fuse to the trailer for the backup lights, this is the circuit that goes to the backup solenoid disconnect that allows you to backup without activating the surge brakes (a pain in the butt for two years now). I have extra fuses but I think I will make a point of disconnecting the trailer each time it goes in the water, I never thought it would matter because the lights are all sealed but something must make it short out.