Lights Won't Go Out

The Lights on my 2001 windstar will not go out. it is the left hand signal and tail light. Has any one seen anything like this before? I have changed all of the bulbs with no result.

Please help.

Keep in mind that all the exterior lamps get a constant 12 positive supply .... its the ground path that gets "switched". ... so all it takes is an erroneous ground.

I'd check the lamp fixtures again.