Ford Mercury Villager 1997 Owner's Manual page 85

NOTE: Be sure that you do not put anything on top of the
photodiode located in the top right side of the
instrument panel speaker grille. The photodiode controls
the autolamp; if it is covered, the photodiode reacts
as if it is nighttime, and the headlamps will be
illuminated.
Autolamp photodiode location
To turn the autolamp off, move the thumbwheel all the way to the
left.
You can set the autolamp so the headlamps stay on for
approximately three minutes after you turn off your ignition. The
farther the thumbwheel is moved to the right, the longer the
headlamps stay on.
Controls and Features
81