This is the key fob you need:
3W73-15K601-AA
FCC ID: CWTWB1U343
Can: 1788a-FWB1U343
Takes a CR2032 Battery
If the FCC / CAN IDs don't match, it won't work.
Programming key fobs from the 2004 Marauder Owners Manual:
Place the key in the ignition and
turn from 2 (LOCK) to 3 (OFF) and
cycle between 3 (OFF) and 4 (ON)
four times in rapid succession within
3 seconds.
After doors lock/unlock,
press any control on all transmitters
(up to four). When completed, turn
the ignition to 3 (OFF).
All transmitters must be
programmed at the same time.
When completed, turn the ignition to the 3 (OFF) position and wait at
least 20 seconds in order to use the recently programmed
transmitter(s).
All transmitters must be programmed during the same programming
cycle. A transmitter that is not programmed within the same
programming cycle will be erased and will no longer operate your
vehicle’s locks. If this occurs, you will have to reprogram all the
transmitters again, as you cannot just “add” a transmitter.