Actually, to monitor the charging system properly, you'd need a voltmeter, an ammeter, and a way of checking the specific gravity of the battery acid. If you're using an internal-regulated alternator, that's about the least maintenance-intensive systrem that there is. You could get away with nothing but an idiot light, like 90% of the new cars have. Just for simplicity, I'd suggest sticking with the dash-mounted ammeter. If you want a voltmeter stashed out there under the hood somewhere just for monitoring the voltage while you're working on it, that would be a simple 2-wire hookup- - - -power and ground.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!