There isn't a fuse specifically for the alternator on a 1997 Ford Expedition. The alternator is controlled by the voltage regulator, which is typically part of the alternator itself (though some models may have a separate voltage regulator). Problems with the alternator usually aren't solved by replacing a fuse.
If your Expedition is having charging problems (e.g., the battery light is on), the problem likely lies with the alternator itself, the voltage regulator, or possibly a wiring issue between the alternator and the battery. You'll need to have it tested by a mechanic or auto parts store.
