To find the relevant fuses, you need to consult your owner's manual. It will show you the fuse box locations (there's usually one under the hood and one inside the car, often in the dashboard) and a fuse diagram identifying which fuses relate to the power top. Look for fuses related to the power top motor, pump, or convertible top system in general. They might be labeled explicitly, or you may need to trace the circuits.
If you don't have the owner's manual, you can often find a PDF version online through a Ford parts website or a Mustang owners' forum. Searching for "1998 Ford Mustang fuse box diagram" should provide helpful results.
