The ammeter going full scale isn't uncommon, as most alternators are capable of 50+ amps right after startup. A good battery should recover from the starter current draw in a couple of minutes and the ammeter should drop back to 20 amps or less. The pegged ammeter is worrisome, but it shouldn't be damaged by the off-scale reading. One sneaky way around the meter-pegging problem is to put a 2" long thin (.020-.030" thick) strip of stainless steel shaped into a horseshoe contour between the ammeter posts as a shunt. It will allow a small amount of current to pass through the ammeter to get some deflection of the needle to indicate charge/discharge, while the majority of the charge current bypasses through the steel strip. The ammeter reading won't be accurate, but they aren't famous for indicating correctly anyway.
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
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