I re-used the heavy duty 100 amp ammeter which came with the truck. It works fine, even though I know most people say to use a voltmeter with alt.
A voltmeter is a little more intuitive to the modern driver about the overall state of the electrical system, while the ammeter will tell you what kind of load is on the battery.
I've seen both types being used with alternators, so to me it boils down to operator preference.
