What alternator do you have? A commonly used alternator is the Delco-Remy, which from the factory was negative ground. (It is possible to have one that has been modified for positive ground.) If you tried to install a negative ground alternator on your positive ground tractor it will immediately fry the alternator.
If you have the common Delco alternator the wiring would be:
#2 on plug to large out put stud
#1 on plug to output side of ignition switch with a diode, resistor, or idiot light in the line.
Output stud to one side of ammeter. Light and ignition switches also go to this side of ammeter.
Other side of ammeter to hot battery post.
If you need to switch to negative ground, ignition coil -- (if it has distributor) goes to side post on distributor.
Connect ammeter so it reads negative with lights on and engine not running.