Have to watch out for those Warrants Unless he was a carrier or Nuke cruiser sailor.
Make sure you get one that you can see in the daylight, I made that mistake.
Could be your Regulator Rectifier, Stator or the connectors at the R/R or one under the battery box going to the stator. The R/R is just below and behind the radiator.
You can find a good T/S procedure here: https://venturers.org/Tech_Library/index.php?action=article&cat_id=002007&id=400
That is a loaded question, if you have never done it before it can take all winter. If it is a first gen case, you may have an issue with parts. It may be quicker and cheaper to get a parts bike or look at pinwall on e-bay.