Short to ground in my alternator?

Well there was “an event”! It blew a 20A fuse, both brake light bulbs, and my ballast resistor a couple drives ago.
That led me to chase down that horn short once and for all. Even took out the front seat and prepared for a fight! Replaced the bulbs, resistor, and up’d the amperage of that fuse to 30. But still get sparks when I replaced the negative battery terminal?? Now I’m at the far end of my fusible link. Thinking I’ve found my smoked gun!
So I get “overloaded” until I crank the meter up to at least 20k. 19+ on that scale, and can replicate it on any ground AND the alternator body…