Your post intrigued me so I did some searching. I found a 2003 Windstar owner's manual on-line. This is a drirect quote:

"KEYLESS ENTRY SYSTEM
You can use the keyless entry
keypad to:
• lock or unlock the doors without
using a key.
• activate or deactivate the
autolock feature.
The keypad can be operated with the factory set 5–digit entry code; this
code is located on the owner’s wallet card in the glove box, is marked on
the computer module, and is available from your authorized dealer. You
can also create your own 5–digit personal entry code.

2003 Windstar
Owners Guide
USA English
Locks and Security
pg 83

When pressing the controls on the keypad, press the middle of the
controls to ensure a good activation.
Programming a personal entry code
To create your own personal entry code:
1. Enter the factory set code.
2. Within five seconds press the 1 • 2 on the keypad.
3. Enter your personal 5-digit code. Each number must be entered
within five seconds of each other.
Tips:
• Do not set a code that uses five of the same number.
• Do not use five numbers in sequential order.
• The factory set code will work even if you have set your own personal
code.
• If you set a second personal code it will erase your first personal code.
Unlocking and locking the doors using keyless entry
To unlock the driver’s door, enter the factory set 5-digit code or your
personal code. Each number must be pressed within five seconds of each
other. The interior lamps will illuminate after pressing the first control on
the keypad.
To unlock all doors, press the 3 • 4 control within five seconds.
To lock all doors, press the 7 • 8 and the 9 • 0 at the same time. You
do not need to enter the keypad code first. Note: The interior lamps
will turn off."

Just need to locate the "computer module"

hope this helps.