For the year it should be a 12 volts ac charging system, in which case the zener and the heat sink should be in the air flow below the Headlight
On The 6volt ac system the system is unregulated, Normal daytime running uses only half the alternator,The switch brings in the other two coils of the alternator when you turn on the lights.
Regulator in the switch ?……Rubbish!
Sorry, well its kind of “in the switch” as the switch is made and is wired to make the correct connections in the different modes, that’s what I meant. I have not seen any documents, manuals, or tech articles that mention a Holder installed 12v regulated system, are there any?