Mercury 2004 Mountaineer Owner's Manual page 91

Locks and Security
5. Turn the ignition from the 1 (OFF/LOCK) position to the 3 (ON)
position. Keep the ignition in the 3 (ON) position for at least three
seconds, but no more than 10 seconds.
6. Turn the ignition to the 1 (OFF/LOCK) position and remove the
second previously programmed coded key from the ignition.
7. Within twenty seconds turning the ignition to the 1 (OFF/LOCK)
position and removing the previously programmed coded key, insert the
new unprogrammed key (new key/valet key) into the ignition.
8. Turn the ignition from the 1 (OFF/LOCK) position to the 3 (ON)
position. Keep the ignition in the 3 (ON) position for at least three
seconds but not more than 10 seconds.
9. Remove the newly programmed coded key from the ignition.
If the key has been successfully programmed it will start the vehicle's
engine and the theft indicator light will illuminate for three seconds and
then go out.
If the key was not successfully programmed, it will not start your
vehicle's engine and the theft indicator light will flash on and off, and
you may repeat Steps 1 through 5. If failure repeats, bring your vehicle
to your dealer to have the new key(s) programmed.
To program additional new unprogrammed key(s), wait twenty seconds
and then repeat this procedure from Step 1.
91
2004 Mountaineer (mnt)
Owners Guide (post-2002-fmt)
USA English (fus)