Your may or may not be able to program this feature yourself on your 99 :?
See my 08/11/05 reply to the
Programing a key fob thread for info on how to determine whether your 99 will need to go to the dealer or not to get it turned on.
Note:
all 98 model D's require a trip to the dealer to turn on/off any of the special features (i.e. auto door lock, horn chirp, lights flash, etc.) or to program a new remote.
As for instruction on "how" to program it, you'll need access to a 99 FSM for those. I did google this and found instruction on how to
add a new remote for 99's that "can" be self-programed but nothing on how to turn on/off all the various features once you get the CTM into
program mode.