One problem related to defogger has been reported for the 1999 Lincoln Navigator. The most recently reported issues are listed below.
On January 15, 1999 we had a snow storm in boston with an outside temp of 5 degrees. We were 4 people in Navigator traveling on highway at speeds of 25 - 35 mph and to my absolute dismay found out that the windshield kept freezing in my line of vision / full defrost & fan speed. Then all side windows iced up & we could not see outside @ all. I have submitted a letter to the pres. Of Ford's Lincoln Mercury division & have not heard from anyone. The dealer tried rectifying it.