Need Gauge help. Thanks

Some general on the ammeter: Lots been written on these, but their exact construction varies over time. Some later models mount through the PLASTIC of the cluster housing, so if that plastic gets warm/ hot..........the ammeter gets loose

There is NOTHING that holds the ammeter together except the nuts. the brass strip "that is" the meter, two studs, nuts, insulating washers. Someone one the www shows soldering/ brazing the studs to the brass, which is a help. If ONE of the (at least 4) nuts comes loose, this generates heat caused by a poor connection, more heat, and then failure.

Bear in mind that depending on what was used, how old, deteriorated, etc, the insulating washers themselves can compress and cause loosness