I have a 2007 Georgie Boy Landau on a Ford chassis also. On ours, the trailer wiring receptacle was not wired from the factory - just loose wires bundled up by the hitch. So, chances are the receptacle was wired at the dealer or later. In 6 years, I can almost guarantee you that the wiring and connections are corroded on the back side of the receptacle.
Do what I just did - remove the receptacle, cut the wires back 6 inches, test for voltage and then put in a new receptacle. For $10 it is much easier than trying to troubleshoot.
