Mercury Sable 1999 Owner's Manual page 69

Controls and features
If the programming procedure was successful, the
new SecuriLock key(s) will start the vehicle's
engine. The theft indicator (located on the
instrument cluster) will light for three seconds and
then go out.
If the programming procedure was not successful,
the new SecuriLock key(s) will not operate the
vehicle's engine. The theft indicator will flash on and
off. Wait at least one minute and then repeat the
procedure from step 1. If failure repeats, bring your
vehicle to your dealership to have the spare
SecuriLock key(s) programmed.
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