you may have a common problem with the ford radio. I too had this problem in my 98 explorer. I fixed it by visiting this site. Hope it helps.
Here is a burb from his site. And yes, I am a happy customer. My name and email are there as well.
These radios may be found in the following vehicles: Explorer, F150, F250, F350, F450, F550, Mercury Mountaineer, Grand Marquis, Ranger, Econoline Van, Crown Victoria, Escape, Winstar, Lincoln Blackwood, Lincoln Town Car, Mazda B-series Trucks, Nissan Quest, and Tribute.
The display problem is common over Ford Explorers including model years 97, 98, 99, and 2000. In 2001 and beyond they have improved their problem, however, there is still an issue in which these radios will also start to fail (or if you have had your radio repaired by the dealer, you're likely to experience the same problem again). The problem is just plain and simple...the radio display goes blank (or fades in and out)...everything works...it is frustrating not knowing what station is playing or what time it is. I consider my own Explorer "pampered"...it's always in a garage when not in use...not exposed to much extremes in temperature, for the most part (though we put a lot of miles on it when it was used in my sales position), so I anticipate this is an even more common problem with others who may leave their Explorer outside.