Hmmm...I'm going through the shop manual and I can't seem to find any circuit details other than the keypad is fed off the Body Security Module and is normally open. I'm assuming that by doesn't light up and not working you've confirmed it's just not the bulb burnt out. May be time for a new one, I'd check out fordparts.com to see if it is replaceable.
NEVERMIND, found it. Here's the diagram for the switch. Probably broken wire in the door, like so many others.
http://www11.zippyshare.com/v/10699871/file.html
BTW, can anybody suggest a decent host for pdf files?