From what has been described, if there was a short in the ammeter, there should be evidence. It should show signs of heat and smell of burnt metal and plastic. Shouldn't have to open it to determine if its OK.

I say this because the fusible link went fast, and it was enough current that even the body ground couldn't handle it. Of course if the body ground wasn't a great connection to begin with, then that does't means so much.

Some place the hot wire had pretty good contact with the body. That is, assuming the engine block connection direct to the battery negative was good.