I guess I really shoud get around to doing that.  Seems to me that I remember the all the parts for a crow-bar system being about $300.   Is that not the case?  I have already modified my alternator so that if I shut off the b-field I can shut down the alternator - do I need to make further internal modifications to the alternaror to use an external regulator?

Dave;

If you have already made the internal mod to the alternator (disconnecting the connection from the output to the voltage regulator) then all you need to do is add the ‘crowbar circuit’ between the field circuit breaker output to ground. The ‘crowbar’ goes to short in the event of over-voltage, trips the breaker shutting down the alternator.  I bought the crowbar circuit from Aeroelectric Connection for about $17 (It’s just a little potted circuit maybe ¾” dia with a couple of leads). But that was then.

I have noted a characteristic of the regulator in the Mitsubishi alternator is that the voltage cycles over small range as you also noted.  Maybe .3 to .5 volts or so, and at a frequency of a few seconds. What I noted prior to replacing my regulator was the range of the cycle increased, as well as the average voltage going up.

Al