Light inside trailer

I bought a new enclosed trailer to haul the motorcycle or 4 wheeler and cannot get the light to light up inside the trailer(it is a brand new trailer I was told the light should work, I will check bulb tomorrow) at all when I plug the trailer into the truck, I have a 2006 Silverado Crew Cab with the round plug in back.

Any suggestions on what to check for?

Most enclosed trailers have to have the clearance lights on for the inside lights to work. They draw the power from the clearance lights. If that doesn't work ask the dealer that sold you the trailer how to get it to work.