a bad amp meter will stop charging. seen it before and it makes sense since all the amps flow through there.

you can verify this by testing the back of the alt, output for voltage, and I bet you see 14 volts for charging. it just isn't making it anywhere.

as said above, if you want to, get behind the dash and check you probably have 14 volts on one side of the amp gauge and nothing on the other.

you can of course bypass it, or run a wire from the back of the alt directly to the battery to get it charging for now.