To find it, you need to consult your owner's manual. This manual will have a diagram showing the fuse box layout and identify the fuse responsible for the fuel pump. The fuse may be labeled "Fuel Pump," but it could also be labeled something more generic, like "Engine Control" or a similar designation.
If you don't have the owner's manual, you can often find a digital version online through a Ford website or a reliable automotive repair manual provider (like Haynes or Chilton). Searching online for "1996 Ford F-250 fuse box diagram" might also yield results. Remember to always be careful when working with electrical systems, and disconnect the negative battery terminal before starting any work.