I also would discourage you from installing an ammeter, especially the kind that routes full power through the gauge. Factory cars have been using voltmeters for 30 years or so now for this reason (and before that few had ammeters either). The voltmeter installation is very easy, you just connect a wire to the place you want to read the voltage and run a small gauge wire to the gauge. And a simple ground.
If you insist on an ammeter, what you should use is one that uses a "shunt". With a shunt type ammeter, the shunt is mounted in the engine compartment somewhere in the run of the alternator/generator output wire. Then 2 small wires run to the ammeter gauge. Stewart Warner used to sell a shunt type ammeter, but I don't know if they still do or not. There were also some factory Chevy ammeters in 60s cars that used shunts.
You can tell all you need to know with a voltmeter, possibly even better than an ammeter. If the alternator is charging correctly, the voltage should be around 14-14.5 volts. If it is below 13.2 volts, the battery is discharging. Once you get down to about 11 volts, there may not be enough power for the ignition, let alone starting if it continues. If the voltage exceeds 15 volts you have a regulator problem and you'll also boil all the water from your battery. What useful information could an ammeter tell you besides those things?