On my 2006 Silverado, there was a wire that had to be connected to the under-hood fuse box before I could run lights in a covered trailer. I had already plugged in a Reese trailer brake and it worked fine. I took it to the dealership and told them what was happening and they told me about the wire and hooked it up in no time and didn't charge me.
When I bought my 2012, we went back to the service department and I ask him about hooking up that wire. He said it wasn't necessary with the new models.