The 60s - early 70s ammeters themselves were reliable pieces, it was the wiring that was usually to blame. If you look any service manual of the era, you’ll see that Chrysler was well aware of the problem - in fact, police, taxi, and fleet vehicles, whose electrical loads were typically quite high (and which vehicles typically had a “fatter” alternator) had the two charging-circuit conductors removed from the bulkhead connector, and its woefully-inadequate 1/4-inch Sta-Kon connectors, and run directly through the firewall (with a simple rubber grommet). If you’ve experienced firewall connector problems, you should consider this mod as an option.

The second plan is to convert to the ‘80s-‘90s style wiring. Simply connect the alternator output stud, via some serious gauge wire (matched to your alternator’s output specs) to the battery stud on the starter relay. But be absolutely sure you splice in an appropriate length of fusible-link wire into this new conductor! Here’s what gauges to shoot for:

Alternator output rating Wire gauge Fusible Link
Under 50 Ampere....................12 ..... 16
50-65 A................................10 ..... 14
85 A.................................... 8 ..... 12
100 - 120 A.......................... 6 ..... 10
With this done, the bulk of the charging system current will no longer flow through the firewall connector - or the ammeter. Obviously, the ammeter will no longer be accurate. The plan here is a simple accessory voltmeter, which should have its positive (+) side wired (with practically any gauge wire) to any ignition-switched 12-volt point, and the negative (-) side to ground.