The number 1 terminal on the Delco alternator is the low voltage source for the pre-excitation circuit. In the IH Scout, this terminal is fed by the resistance wire which is switched on and off by the ignition key. When the ignition is turned on, the alternator's rotor field is charged so when it(the rotor) starts spinning, the stator can begin producing current.

The number 2 terminal provides the internal regulator with a battery

reference voltage. This allows the regulator to continuously monitor the battery voltage and control the rotor's field strength, which in turn controls the alternator's output.

Of course the "BATT" terminal is the alternator's output to charge the

battery, which gets routed through the ammeter.