Leave the wire off that goes from the starter cable to the ammeter, try to connect the battery cable, and see if the short goes away. It's possible there's a short in the starter. If isolating everything but the starter stops the short, it's somewhere downstream- - - -the ammeter or beyond.
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!