Buick 1998 Century Owner's Manual page 118

Twilight Sentinel
Twilight Sentinel provides a period of exterior
illumination as you leave the vicinity of your vehicle.
The feature is activated when your vehicle's headlamps
are on due to the automatic headlamp control feature
described previously in this section, and when your
vehicle's ignition is turned off. Your headlamps will
then remain on until the headlamp switch is moved from
OFF to the parking lamp position or until a 90 second
illumination period has elapsed.
If you turn off the ignition with the headlamp switch in
the parking lamp or headlamp position, the Twilight
Sentinel cycle will not occur,
You can customize the vehicle to activate the Twilight
Sentinel when your vehicle's ignition is turned off under
the conditions described above, or you may choose not
to activate this feature under any conditions. The
enableddisabled state of this feature will be toggled
when you perform the following sequence with the
doors closed and the ignition key in RUN:
1. Press and hold the power door lock switch. While
holding the door lock switch, cycle the headlamp
switch on and then off two times.
2.
3.
Release the power door lock switch. These
operations must be carried out in a time period of
less than 10 seconds, followed by a delay period of
no more than 10 seconds.
Then, press and hold the power door unlock switch.
While holding the door unlock switch, cycle the
headlamp switch on and then off two times. Release
the courtesy door unlock switch. These operations
must be carried out in a time period of less than
10 seconds.
After releasing the door unlock switch, a single chime
will be heard if the Twilight Sentinel function has been
disabled; two chimes will be heard if the feature has
been enabled. Disconnecting the vehicle's battery for up
to a year will not change the programmed operation of
this feature.