There were TWO versions of the key pad systems...on is a "bolt on"
wired system that was delivered from the factory.
the other type is a STICK ON version that is self contained and runs
on a watch type battery.
the Bolt on version came w/ a small white laminated paper "wallet" card
that has a "MASTER" number printed on it...this MASTER number can not
be erased (you can create your own code, but the master is perminant and
can always be used).
Ive HEARD (but never confirmed) that the "MASTER" access code number is also
printed on the firewall (inside the truck) behind the radio...again rumor only as
far as im concerned.
the bolt on version of the key pad sits in a small "recess" thats in the metal of the
door.
the stick on verison sticks off the door quite a bit more...its method of operation
is nothing more than a key fob that has more buttons (w/ numbers on it)...and i believe
it is programed using the factory remotes.
these might help -->
Ford Keyless Entry Key Pad Installation - Article #1
WikiAnswers - Keyless Entry Keypad FAQ Ford Explorer
heres what the stick on version looks like -->
Conveniently unlock your vehicle without your key or keyless entry remote. No wiring necessary – programmable, backlit keypad tunes to the same frequency as your transmitter. No-drill installation. Comes with two covers: one is primed (paint to match); the other has a black textured finish. For vehicles equipped with factory remote keyless entry. Works with 2005 and up Ford and Lincoln Mercury vehicles! (Does not work with Hybrid vehicles.)