Depending the year/model/dash the ammeter is fairly common to just as rare as any other one year only part. For example the bulkhead multi-connector on your '65 is different than 64 or 66.
They don't age out and there is only one moving part - the needle, so they don't wear out mechanically as far as I've ever seen.
Ammeters, or more commonly the connectors, can get damaged by water (leaks in dash, windshield or cowl).
They can also be damaged electrically when overloaded. If the needle swings 1/2 way toward either charge or discharge, that's 20 amps going into or out of the battery. That's about the max the circuit should ever be subject to, AND 20 amps for long periods of time will heat up and damage connectors. If you have a damaged battery or alternator feed connection on the bulkhead, this is probably the reason. Twenty amps or more continuous to the battery for recharging means the alternator is sending that
plus whatever is needed to run the engine, brake lights, turn signal etc.
The rest of the instrument panel is isolated from the ammeter. So depending on the cause of the ammeter damage it is likely the rest of the instrumentation and lighting is OK. This post
has photos and a diagram.
If you have to bypass the ammeter, then it is advisable to have some way to judge the electrical system. Underdash ammeters used to be common in aftermarket gage sets (as many of Mopar's competitors didn't provide gages on their base models). Easier generally is some sort of voltmeter. Even your hand held multimeter. Run the engine and make sure the alternator is producing power around 14 V and it doesn't follow the engine rpm.
Without an ammeter, we can assume the battery is getting recharged if the alternator is producing power at 14 Volts.
However don't know the charge rate. That requires an ammeter.
