Ford 1999 Crown Victoria Owner's Manual page 97

Automatic locking mode
In this mode, the shoulder belt is automatically pre-locked. The belt will
still retract to remove any slack in the shoulder belt.
The automatic locking mode is not available on the driver safety belt.
When to use the automatic locking mode
When a tight lap/shoulder fit is desired.
Anytime a child safety seat is installed in a passenger front or
outboard rear seating position (if equipped). Refer to Safety
Restraints for Children or Safety Seats for Children later in this
chapter.
How to use the automatic locking mode
Buckle the combination lap and
shoulder belt.
Grasp the shoulder portion and
pull downward until the entire
belt is extracted.
Seating and safety restraints
97