No power in the car

The condition of both the terminals and the ammeter studs don't look good.
The studs you should be able to clean up.
Make sure the studs aren't loose. And if there's no resistance between them then the ammeter should be OK.

I don't know how to replicate those heavy seals over the terminal connections.
Someone else here might. So if you have to cut them open to inspect or replace, all I can suggest is heat shrink.