The location of the rear window defroster fuse in a 2004 Ford Explorer isn't consistently documented across all trim levels and models.
You will need to consult your owner's manual. This manual will have a fuse box diagram showing the location of each fuse, including the one for the rear window defroster.
The fuse box is typically located either under the hood or inside the vehicle, often in the dashboard or under the steering wheel. Your owner's manual will tell you exactly where to find the fuse box and how to interpret the diagram.