[SFfiredog]

The big bump...
Check to make sure the positive cable on the battery isn't touching a gound source, or one of the larger power wires isn't worn though and grounding to some metal source.
The ampmeter is usually wired directly to the alternator output power wire so it usually will cook first.
I have a feeling something could be shorting to ground.
Also, like I mentioned, a loose gound will cause excessive resistance, which is HEAT... ooh stinky, stinky, melty, melty, smokey, smokey which is of course, all bad.
--Mike