Its your tractor and your call as for what gauges you install, however for no more then the cost,,,,,,,,,ease of installation,,,,,,,,,conforms to originality n looks correct n satisifes "Correct Police",,,,,,,better indicator of actual charging system operation,,,,,ID PERSONALY PREFER AN AMMETER.
My reasons are the voltage is like 12.6 volts setting but at fast RPM if shes charging good the battery voltage only rises to like 13 to 14 and a lil over AND THE RESOLUTION AND METER MOVEMENT IS NOT ALL THAT GOOD AND INDICATIVE AS THE INFORMATION AN AMMETER CAN PROVIDE IN MY OPINION
Am ammeter, however, would read dead center setting,,,,,,,,swing to - discharge even if only a few amps of discharge occurs,,,,,,,,,,have good resolution when running from like a few up to 10 to 20 amps of charge at fast RPM AND JUST PROVIDES MORE DETAIELD MORE PRECISE ACCURATE INFORMATION OF WHATS HAPPENING IN MY OPINION VERSUS A LESSSER RESOLUTION VOLTMETER.
A slow discharge (like a minor high resistance short) wouldnt hardly if at all be even noticeable on a voltmeter and shes gotta be at decent fast RPM to raise battery voltage to 14.2 etc but thats NOT as readable on a gauge then an ammeter that has a full easily observeable needle swing from - 20 to + 20 (0r 30) amps charge.
That slow few amps discharge (to run battery down if she sets several hours) is very noticeable on an ammeter but not near as noticeable/readable on a voltmeter cuz a few amps trickle discharge on a battery dont drop the voltage down much (if at all) from the normal setting 12.6 volts
OKAY RANT IS OVER LOL its your call and Jim has told ya how to wire it up but give me an ammeter any time on the old tractors (THEY JUST ARE RIGHT N LOOK BETETR LOL) and I can easily observe its neelde n tell you much better the charge or discharge rate n whats really happening VERSUS that voltmeter which is more for modern autos with alternators
Best wishes, either will fit in slot n will work if thats your preference.
John T (NOT any Correct Police buttttttt believe an ammeter is much better)