The voltmeter is easy to wire - negative to ground, positive to any convenient switched +12V feed - mine is wired to the accessory line, which is where every factory voltmeter I've seen was wired.
The ammeter is going to be a lot more challenging - first you'll need a center zero ammeter with a rating not less than the output rating of your alternator, and I have not yet seen an automotive ammeter rated at more than 60A. For this reason, one of my vehicles has an ammeter and the other, a volt meter.
The ammeter must be wired with the appropriate sized cables between the battery positive (the ammeter positive terminal connects to the battery positive terminal) and the vehicle's electrical system - the only device which connects directly to the battery positive, bypassing the ammeter, will be the starter, and if you have one, a winch.