If you purchased additional keyless entry remote transmitters, or replaced a lost keyless entry remote transmitter, you must have ALL of the keyless entry remote transmitters for the vehicle present during this programming. ALL of the keyless entry remote transmitters must be programmed at the same time.
The remote anti-theft personality module erases all previous keyless entry remote transmitters from memory when the keyless entry remote transmitters are programmed or reprogrammed. The remote anti-theft personality module can store up to four keyless entry remote transmitters in memory.
To program (or reprogram) keyless entry remote transmitters into the remote anti-theft personality module, perform the following steps:
1. Make sure that the anti-theft system is not armed or triggered.
2. Turn the ignition switch from OFF to RUN five times within 10 seconds, ending in RUN.
If the remote anti-theft personality module has successfully entered program mode, it will lock and then unlock all doors.
3. Press any button on a keyless entry remote transmitter, and the doors will lock and then unlock to confirm that each keyless entry remote transmitter has been programmed.
If the door locks do not respond for any keyless entry remote transmitter, wait a few seconds and press the button again.
4. Turn ignition switch OFF (or wait up to five minutes after Step 2) to exit program mode. If a new set of keyless entry remote transmitters have been programmed (or reprogrammed), the remote anti-theft personality module will lock and unlock all doors one last time to confirm.
As I just found out the following page needs an edit.
At least on a 99 it takes 8 times of cycling the ignition within 10 seconds. I tried 5 times until I was blue in the face. Then I came across directions on TCCA that said 8 times and presto! My 96 isn't easily accessible at the moment so if one of you could go through the process on either of your cars you could determine if it is just 8 times for 98 and up, or if it is 8 for all years.
Hope that helps,