When I added extra gauges to Lucky, an ammeter was top of my list of priorities too. I was persuaded to have a voltmeter instead, largely on the grounds of ease of wiring it in (Volts are everywhere the same - amps you have to be choosy about where you tap in). I was somewhat reluctant (
electrical engineers joke) but now that I'm used to it I think it actually tells me rather more about what is going on. Essentially, if the volts are above 12V I have confidence that the battery is being charged. If they are less I know that the regulator and generator haven't caught up yet. Plus you can see exactly how the regulator is regulating as the revs rise and fall.
So my advice would be to go for a simpler wiring job and get rather more information back. Fit a voltmeter.