Wondering if you ever came to a conclusion to your interior light problem. I have an 05 King Ranch and it does EXACTLY the same thing you are stating. Do you have a Ford remote start? I have looked in my dash and aside from the switches all that is up there is the remote start module and there is a relay mounted to the bottom of the metal bar above your left foot. I also ran outside one night when the gremlins were at it and pulled out the light switch and dimmer and disconnected the harnesses from the switches, with no change. This leads me to believe the relay may be the problem since the switch sends the current to the relay to activate the lights. If it was the switch the lights would go off as soon as the harness was unplugged since the power connection to the relay would be terminated. I am gonna call up my ford parts guy and beat his ear a little tommorow about the relays. Also, discovered this little treat which is apparently a problem also, if you have a center console shifter and the light appears to have gone out for the shift position indicator make sure you take off the top panel and take a peek. I found out that my socket deformed and dropped out of the housing allowing it to rest against the inside wall of the console. That little bulb puts off some heat and actually melted a few marks into the plastic. If left alone it would eventually work its way thru the plastic and or could start a fire........so check it out if it applies.....