Alternator troubles /HELP

[Andrew <lynx@domain.elided>]

Hey guys,
  I've finally made up my mind. I NEED to get the IH ('69 1200 3/4 4X4) fixed once and for all.
I still drive it around but the alternator is giving me trouble and I just keep putting it off. 
  It surges up and down. (so bad my lights get bright and dim ) When the battery is almost drained though sometimes it seems to charge right. 
   Could it be the little black "F" (field ?) wire?  Is that a "sense" wire?
Which prong on the voltage regulator does that go to?  When I tried proding them all black wires lit up, not just the sense wire on the voltage regulator. Therefore I don't know which terminal it's on. 
  Also, How hard would it be to convert to a 1 wire alternator??? Could this be done on mine?  Will it solve my problem???
  I've replaced my voltage regulator, alternator, cleaned the grounds etc. no luck yet.
Thanks,
Andrew Thomas
'69 IH 1200 4X4
345, 4-speed, 4:10's