Deactivating/activating the autolock feature...
Before following the procedure, make sure that the ignition is OFF and all vehicle doors and the liftgate window are closed.
You must complete steps 1-5 within 30 seconds or the procedure will have to be repeated. If the procedure needs to be repeated, you must wait 30 seconds.
1. Turn the ignition key to ON.
2. Press the power door unlock control three times.
3. Turn the ignition key from ON to OFF.
4. Press the power door unlock control three times.
5. Turn the ignition back to ON. The horn will chirp.
6. Press the unlock control, then press the lock control. The horn will
chirp once if autolock was deactivated or twice (one short and one long
chirp) if autolock was activated.
7. Turn the ignition to OFF. The horn will chirp once to confirm the
procedure is complete.
Also, if your vehicle is equipped with a coded-key anti-theft system. Only the correct key will be able to start your vehicle. If your keys are lost or stolen, you must take your vehicle to a Ford/Lincoln-Mercury dealership for re-programming.
Programming additional keys If you need additional keys electronically coded for your vehicle, spares can be purchased (a maximum of 16 keys can be programmed). To program a new key, perform the following procedure:
1. With the coded key in the ignition, turn the ignition from ON to OFF.
2. Within 15 seconds of turning ignition off, insert the new coded key
into the ignition and turn it from OFF to ON or START. If successful, the
THEFT indicator light will illuminate for two seconds. Repeat procedure
for all new keys.
If key coding fails, the THEFT indicator light will flash.
Coding failure can be caused by any of the following:
² The new key was not inserted into the ignition within 15 seconds.
² 16 keys have already been programmed.
² The new key does not have an electronic code.
Other details can find in the 1998-Lincoln-Navigator-Owners-Manual

30 minute reset turn key on ten minutes security light will go off turn off back on three times it ctanks