It aint a voltage regulator; just a cutout. Third brush and S/W charge been extensively covered in numerous posts. John Cornforths diagram just updated and better than ever on the Dorset Club site, although for a Ruby and not applicable in every detail, is about the best guide you will find. (The F1 terminal may not be connected in earlier but it is unused anyway). If the dynamo and/or wiring is non original the Cornwall Club article Charging refresher may untangle.

Johns diagram gives the internal connections. The handbook wiring diagrams will pick up the slight external differences for 1933.

Location: Auckland, NZ

Thanks Bob

I think that, in another post, Peter CRDC confirmed that the SB5 is just the solenoid within that you will want to look at - i.e. its the "CF3" cutout.

It paired with a C35A dynamo with an external box resistance on it... the external box became part of the cutout and became the CFR.

So care when pairing units as you might not have enough things to make everything work if you get the wrong dynamo!

the Dorset diagrams are good. Good to hear the Cornforth is improved.... minor clarification on the PLC switch makes it even easier to understand. And the new drive-thru MacDonalds between the F1 - F2 bridge is a great idea!