Ford CMP Voltage Regulators

[BCA]

The wiring schematic in MB-F1 shows the battery as having a positive ground. Various Ford parts books show a choice of a voltage regulators with either positive ground (regulator C11A-1505) or a negative ground (regulator C11AS-1505).
I can't see any discussion in the manuals about the regulators being either positive or negative ground. Why were there these variations.
If your ammeter reads backwards then it would indicate you have chosen the wrong battery terminal as your ground.
Can anyone clarify this issue.
.... Brian