Here is some info I picked up from one of the SC sites....I can't remember who wrote it so I can't give the proper credit, sorry....
This applies to 89-93 climate controls. If one of the bulbs burn out behind the buttons it is easily replaced for $1.49 You have to use a ford radio removal tool (or go to WalMart and get a DIN removal tool set from the "car stereo" dept.) to get the climate control out of the dash. It may not be necessary to unplug anything from the back if you can pull it out far enough to get to the bulbs. You will find 2 grey plugs in the top of the unit. Use a flat blade screwdriver to turn the plug counter clockwise 1/4 turn then pull the plug out of the unit. You need to purchase from Radio Shack or any electronics store a "Micro Lamp" 12 volt / 60mA with a Wire Terminal base. the wire terminals push down through 2 holes in the bottom of the grey housing that holds the bulb then twist on 2 tabs.
A good tip is to take a bad bulb with the screw-in holder with you when you go on your search. I got a couple of bulbs from an autoparts house that were close but not exact replacements. The bulbs fit in the holder and so far are working fine. Make sure you screw in the holders all the way when re-installing or they will flicker on and off when you drive over bumps. Very annoying....