The 72 had a separate regulator. The '93 has the regulator built into the ECM. The field wire you are referring to is the regulator wire. SOOOOOOOO on my '95 the regulator/field is pin 20 on the ECM. The other wire goes to ground.
The large output wire goes to the PDC, then to the battery. The field voltage can't be successfully measured at is a Pulse Width Modulated signal to better control the alternator. A #4 wire can be added to the alternator to run to the frame if one isn't provided.