I have an '07 F150 Super Crew and a new '07 Featherlite 1610 tandem v nose trailer. Both have the usual 7 pin wiring connectors. Everything lights up fine on the trailer except the interior light. I confirmed the light does have a good bulb in it.
Upon investigation, I found that there is no power (on the truck side) at the center pin of the connector and at least one other (can't remember which. Both of the dead pins are marked for "aux" and one includes the breakaway, so that may not be charging either.
My trailer dealer mentioned that sometimes there is a fuse missing from the factory, I should just look for the empty and put one in. Well, all the fuses are there.
What's next?

Since your truck is still under Ford's warranty ... Call the truck dealer and ask.