Have you considered the possibility that the ammeter is shorted internally? Disconnect everything attached to the ammeter EXCEPT the wire to the starter cable, and see if the breaker trips when you connect the battery cable. If it doesn't, them touch one wire at a time of the ones you disconnected until you find the circuit with the short. "This ain't rocket surgery"- - - - - -all it takes is a little bit of logic and common sense!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!