Wiring in a volts gauge.

The "factory connection" for your ammeter are 2 ring terminals, separate from the rest of the dash. You can just connect together, but better to run a bypass in the engine bay. This would be from the alternator output (big stud) to BATT+. Most people go to the big stud on the starter relay instead of BATT+. However, you do it, don't leave any uninsulated terminals hanging w/ 12 V on them. For the new voltmeter, connect + to IGN1 off the starter switch or ACC at the fuse box. Connect - to a good ground.

Many here say "I don't know electricity", but they were the same ones who didn't pay attention in science class, saying "I'll never use this". Ditto whenever they need a little algebra to understand dyno charts. It is simple to find tutorials on the web, try wikipedia and youtube.