Constant voltage regulator???

[M6csi]

Just bought the oe BMW voltage regulator (12311735742) for the 1991 850. This regulator has a ceramic guide pin on the back, whereas other (most) Bosch regulators don’t. According to the workshop manual, this is a constant voltage regulator (‘mechanically encoded’) and must never be interchanged with other non-coded regulators. What is the difference and what does the ‘constant voltage regulator’ do. Thanks!

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[shogun]

I asked the electronic expert from the E32 forum, reply from E32Fan: I ran across this issue recently. I have two used alternators, both from 735iL M30 engines. One alternator/regulator (1197311038) has the porcelain "pin", and the other does not.
I checked the Bosch description in "AUTOMOTIVE ELECTRIC/ELECTRONIC SYSTEMS" 1995 edition, and it does not mention "constant voltage" alternators. But every alternator maintains a constant voltage - that's the whole idea!
The workshop manual warns: "The constant voltage regulator must never be installed in vehicles whose battery is in the engine compartment. This would result in damage to the battery." So Bosch sees a difference when the battery is in the engine compartment close to the alternator, or far away under the rear seat or trunk. Bosch designed the "pin" for a purpose and it should be respected in maintenance. My guess is that either type will work fine when the battery is remote. You can buy boosted (14.3 volt) regulators, I learned.