Does anyone know what the output is on the 3rd smaller wire is on the alternator? On mine it is showing about 0.1V does that sound right?

Is that not the one that goes to the charge bulb?

Have a snoop around this web site see if it helps

http://www.mgb-stuff.org.uk/electricstext1.htm#charge

Adrian

^ ditto, goes to the charge light and needs to be supplied 12v to initiate charging.