It's a combination rectifier and regulator. Two devices in one box.
As he says, there will be 2 silicone controlled rectifiers (SCRs) in the regulator, on one for each yellow lead. The SCRs are connected between the yellow lead and the case.
Unlike normal rectifiers SCRs only turn on when told to, that's why you need 12 Volts. There is an electronic circuit inside the regulator that uses the 12 Volts to first of all determine the Voltage in the battery and then turn on the SCRs if needed.
The Alternator has 2 sets of coils, one for each yellow lead, when the SCRs are turned On first one coil / SCR then the other push current into the battery. When the battery is fully charged the SCRs start to skip the odd half cycle.
These regulators are similar to the Ducati Energias in many ways but have less parts.
