Unfortunately, that ammeter is beyond repair. That stud is pressed into a shunt that is very sensitive to resistance in the connection. You'll hear a lot of advice in about 3- - -2- - - -1 seconds that using an ammeter on 12 volts will cause something akin to the Chicago fire. I print those comments out and use them to fertilize my garden. Find yourself another ammeter, and rig a second shunt to bypass some of the charging current around the meter movement to keep it from pegging out for the first few seconds after startup. Drop me a PM and I'll describe how to do that.
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!