I know that a one wire alternator hooks directly to the battery, but what happens to the ammeter on the dash? Do I let it read zero all the time?

 

Unhook it and run an aftermarket voltmeter. Most good aftermarket alts will run higher voltage than the factory ammeter was designed for, so there is the possibility of an electrical fire if it overheats, but it's a remote one. But basically with the internally regulated 1 wire, the factory ammeter won't function properly.