What fuse is to be replaced when the Brake Lights don't work on an 89 Ford Econoline Blinkers Hazards and Park Lights work?

The problem might not be a fuse. There is a switch which activates the brake lights when the brake pedal is depressed. This switch is usually mounted under the dash, near the top of the brake pedal lever. Insure that this switch is free to move physically, and test it to see if it is switching electrically.