alternator is blowing the engine harness fuse!

What kind of alternator? One wire? Mopar? ?????

If it's an external regulator type (like factory Mopar) you either have a broken insulator at the output screw, or "bad stuff" wrong in the alternator, IE bad diodes, etc

If this is an internal regulated and or "one wire" setup, it could be something lesser wrong, IE "diode trio" (in some) or bad regulator. And of course it still could be as above.