2008 Chevy Trailblazer trailer wiring

Bought this trailblazer 2 months ago and have a problem with connecting the wiring to make the running lights work for my boat trailer. I have the turn signals and hazzard lights working, but have no power to the (brown wire) at the plug in adapter on the vehicle. I have checked the fuses under the back seat and under the hood several times and all are good, but have a question about the special square fuse for the trailer in the fuse panel under the hood (looks to be good but?). Just ran across someone's note on the net about having to connect this brown wire, as it was not connected by the factory? Can you help ! Dan