Ammeter to voltmeter conversion

Just my personal opinion...

If I was to do a Ammeter to voltmeter swap I would cut the arm off the stock gauge and glue it to the voltmeter gauge. I would also use the stock face plate and tune the voltmeter so that at whatever normal charge voltage you have the needle is centered. If it is significantly to the right it is over voltaging significantly to the left and undercharging.

Another option would be to get a remote Ammeter that uses a magnetic pickup and put it on the battery feed.

Lastly if you do run a dedicated charge wire directly from the alternator to the battery post on the starter relay AND assuming your Alternator feed to the Ammeter and battery feed to the Ammeter wires are good and the connectors at the bulkhead are good, by leaving the stock wiring in place ( at alternator and starter post) you cut the current through each connector in half.