Mercury 2002 Cougar Owner's Manual page 76

Locks and Security
A second key on the same key ring as the coded key
If any of these items are present, you need to keep these objects from
touching the coded key while starting the engine. These objects and
devices cannot damage the coded key, but can cause a momentary "no
start" condition if they are too close to the key during engine start. If a
problem occurs, turn ignition OFF and restart the engine with all other
objects on the key ring held away from the ignition key. Check to make
sure the coded key is an approved Mercury coded key.
If your keys are lost or stolen you will need to do the following:
Use your spare key to start the vehicle. or
Have your vehicle towed to a dealership. The key codes will need to
be erased from your vehicle and new key codes will need to be
re-coded.
Replacing coded keys can be very costly and you may want to store an
extra programmed key away from the vehicle in a safe place to prevent
an unforeseen inconvenience.
The correct coded key must be used for your vehicle. The use of the
wrong type of coded key may lead to a "no start" condition.
If an unprogrammed key is used in the ignition it will cause a "no
start" condition.
Programming spare keys
A maximum of seven keys can be coded to your vehicle. Only
SecuriLock keys can be used. To program a coded key yourself, you
will need two previously programmed coded keys (keys that already
operate your vehicle's engine) and the new unprogrammed key(s) readily
accessible for timely implementation of each step in the procedure.
If two previously programmed coded keys are not available, you must
bring your vehicle to your dealership to have the spare coded key(s)
programmed.
Please read and understand the entire procedure before you begin.
76