Keypad will function to lock doors by pressing 7-8 and 9-0 together, as stated in manual, but will not accept factory code or my personal code to unlock doors.Car had new spark plugs put in last week,not sure what relationship that would have with
keyless entry system.

My grandfather had a1992 Towncar, l have a friend with a 94 Grand marquis (both of those had the keypad) & l own a 1997 Crown vic Lx (No keypad) but the (remote clicker) . The power lock control system failed on all 3 & left me stranded due to the engineers dumb idea of wiring it into the ignition system. Now the power locks dont work at all. l doubt the spark plugs have anything to due with this, because these cars r notorius for this problem, & l believe certain years had bugs in the programming code.

l have owned over 15 to 20 Lincolns and Mercury is with keyless over the last almost thirty years and never had a problem. But when they change your plugs they may have disconnected your battery and that will wipe out your personal code but the factory code should always stay. Double check yourself that you are keying in the correct factory code then if so go back to the dealer.

Key pad has a button stuck or broken, usually caused by pressing buttons too hard