The point is its not the ammeter.
its when the wire insulation chafes against a ground,
or the ammeter connections get loose.
Both of which are issues with routing and wire support, and often someones messing around up there.
Anotehr failure cause mentioned by Redfish, that he had personally seen on certain years '73, '74) is from leaks at the cowl area - windshield or wiper pivots. This causes corrossion. In fact he just warned someone two days ago that joining the ammeter wires doesn't solve the problem. All it does is confirm his other test which showed the ammeter was damaged. Note the ammeter did not explode or even light up.