Regulator for 12 volts

[Boxprod]

This is just offering my experience in case it's helpful to others....
My 1974 350 Mk3 is now happily wandering the Cornish roads, and occasionally further afield, running on a simple 12-volt conversion. As you may have read, I've retained the original Motoplat system, refurbished by Steve at Bradford ignition (actually in Cornwall), and all seemed well. Until it didn't.
I've put a small digital voltmeter in the headlight case, so I can see how things are going, and a few days ago it started showing erratic voltage, from 12.1 to 14.8, apparently not having anything to do with load or revs.
Testing the alternator stator is easy (Google it if you need), and the Motoplat thing is giving 20v AC at idle, rising to 60v AC at 3,000rpm. So all well there.
I'd used a cheap Chinese reg/rec (less than £15 on eBay or Amazon) of the 5-wire type, and that seemed OK, but it appears it really couldn't cope with the stress of a 50-year-old alternator, and was getting hot and bothered despite being mounted in a good air stream. Melted connectors gave the game away.
Research revealed that the Chinese regulators are old-style shunt regulators, which simply "shunt" extra voltage to earth, and can therefore get quite hot. It's worth saying that the manufacturers only really claim these things are suitable for 125s, which presumably have less powerful alternators, but what do I know?
Later technology is known as MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and this switches off the charging voltage when the battery has enough, therefore getting less hot. MOSFET kit is a bit more expensive, but probably worth it.
So I've fitted a MOSFET regulator from Electrex https://www.electrexworld.co.uk/cgi-bin/sh000001.pl?WD=universal%2012v%20regulator&PN=RR122%2Ehtml#SID=439. This only has four wires, simply because it senses the voltage from the battery and therefore doesn't need the fifth wire from a switched + supply.
This is a much more robust bit of kit, and the voltmeter shows a more stable rate than the cheaper Chinese effort, so that's a result.
Enjoy the summer, if you're in the Northern hemisphere.
Pete.