Your vehicle comes with three coded keys; additional coded keys may be
purchased from your dealer. The dealer can program your spare keys to
your vehicle or you can program the keys yourself. Refer to the
Programming spare keys section in this chapter for instructions on how
to program the coded key.
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Programming spare keys
A maximum of eight 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
take your vehicle to an authorized Ford dealer to have the spare coded
key(s) programmed.
--2004 Lincoln LS Owner's Guide, pp.150-151