If you TRULY have a factory 65A option, then part of the problem is "already fixed"
First WHAT ARE WE WORKING ON this is important, what year model?
If you have a 73/ earlier, go to MyMopar and download a factory service manual for free
If you have a 74, contact me about a service manual also for free + a small amount of postage
Start by reading this article:
[URL]http://www.madelectrical.com/electricaltech/amp-gauges.shtml[/URL]
IF YOU REALLY HAVE the 65A factory option, part of your problem is "fixed." This is because the ammeter wires had a "partial" bypass by running the wiring through the firewall with separate grommets, instead of depending on the bulkhead connector.
With a "stock" system the general idea of the problems are this:
1...Generally the wiring for the charging system was simply too darn small for anything larger than a 37--40A alternator
2...The connector terminals in the bulkhead connector were NEVER intended for anything over about 20A and "iffy" at that
3...The ammeter itself can "get loose" and lose connection, generate heat and oxidation and "snowball" (fireball) until it's a total failure
4...Present day folks adding larger alternators to old, ratty wiring PLUS the wiring was never intended for larger ones in the first place, is "guaranteed failure"
IF the wiring is already damaged, you maybe faced AT MINIMUM with pulling the engine bay affected harness out AS WELL as the under-dash harness, unwrapping it, and possibly replacing some wires or at least re-making some connections
You can buy terminals to replace the bulkhead connector terminals.