Ford 1999 Taurus Owner's Manual page 125

3. To unlock the trunk, press the 5/6 button
within five (5) seconds of unlocking the driver's
or passenger's door, or re-enter the code to
open the driver's door, then press 5/6.
As long as the driver's door has been unlocked first,
you can open the passenger door or the trunk in
any order.
Locking the Doors with the Keyless
Entry System
Along with unlocking your doors, you can use the
keyless entry system to lock the doors.
To lock all of the vehicle's doors at the same time,
press 7/8 and 9/0 at the same time. It is not
necessary to first enter the keypad code. This will
also arm your anti-theft system (if equipped).
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Autolock
The Autolock feature will automatically lock both
doors when:
the ignition key remains in the ON position
driver's and passenger's doors are closed
a door is opened and then closed
the vehicle is in a forward gear, and
you exceed three mph (five km/h).
If you do not want to use the Autolock feature, it
can be deactivated by using the driver's settings
menu in the Message Center.
Programming Your Own Entry Code
You can program a personal code to unlock your
vehicle. This code does not replace the permanent
code that the dealership gave you. Use your
personal code in the same manner as you would
your original code.