I would NO WAY run that big wheel on factory wiring. Read the MAD article and "do" the bypass.
The factory knew full well that these bulkhead connectors are weak----they bypassed 'em when supplying 60 or 65A optional ammeters. These are known variously as "fleet" or "taxi" wiring.
The MAD article, a good read whether or not you bypass the ammeter:
Here's an EXCELLENT thread. Read all three pages. This details how easy it is to pull the ammeter apart and mount a voltmeter in it's place. This covers several styles of instrument clusters