A good number of modern production passenger vehicles use some sort of computer
to control the headlights, parking lights, turn signals, dome lights and
other illumination. 1995 and later ford crown victorias are no exception,
the only exterior lighting that is not computer controlled is the brake lights
and spotlight (if so equipped). The factory service manual calls the computer
in question a "Lighting Control Module" (LCM) but many mechanics refer to
it as a GEM (Generic Electronic Module). Has some nice features, like if
you accidentally leave the parking lights on when you shut off the ignition,
the car will shut them off automatically after 30 minutes. Same is true if
you leave the door ajar, the computer will automatically turn the domelight
off after a predetermined interval so as not to drain the battery.
Opening a door is only an input to the computer, the computer then decides
how to act on the output. In the case of police interceptors with "Dark Car" mode enabled, the response is to ignore
the open door signal and not turn on the domelight. Turning on the switch
to your headlights or parking lamps is likewise just a input to the computer.
Below are a couple pictures of the circuit boards inside the lighting control
module case. The smaller relay is for the turn signals, the other larger
ones are for the low beam headlights, high beam headlights, parking lamps
and demand lighting output. The round device labelled "TMX-06 95'G" is the
seatbelt/headlight/airbag audible warning buzzer.
