Here's some info on the PATS system:
On-Board Programming Method "C"for Ford keys (Later 1998-newer Ford, Lincoln, Mercury)
If you want to initiate a new master key...
1. This requires that the vehicle be connected to special dealer equipment. There are two ten minute delays involved while this device erases all existing key programming and sets up the vehicle computer to accept new key codes. Two new keys should be ready because the system requires a minimum of two keys in the program. After the first two keys are programmed, additional keys can be entered individually by following the instructions for adding duplicate keys (below).
If you want to add a key...
**You must have two original keys to perform this procedure. If you only have one key, you WILL have to take it to the dealer to get it programmed**
1. Insert and existing (working) key into the ignition cylinder.
2. Turn the ignition cylinder ON (RUN) and back to OFF. Ignition should stay on for at least ONE SECOND.
3. Remove the existing key and, within TEN seconds, insert a second working key and turn it to ON (RUN) and the back OFF. Ignition must be in ON for at least ONE second, but no more than TEN seconds. Remove the key.
4. Insert the new key before TWENTY seconds have elapsed and turn it to ON (RUN). Leave it the ON position for at least ONE second and turn back to OFF.
5. The security light will light up for THREE seconds to indicate that the new key has been successfully programmed.
6. To program additional keys, repeat steps 1 through 5