2001 Ford Focus Turn Signal Mechanics

I have a 2001 Ford Focus wagon. I bought it used; the signalling switch has never shut off automatically after completing a turn.

Now I am thinking of selling this great car, and I’d like to make sure that everything is working. So after looking through Chilton’s and Hayne’s repair manuals I went to a local Ford parts dealer and bought a non-returnable $75.00 signalling unit. I installed the damn thing and the signalling switch still didn’t automatically turn off after completing a turn.

What gives? What am I missing here? Is there some kind of trick involved in the repair of signal lights that Ford shares only with bonafide mechanics? Help!