One of the problems with older bikes are the ,"Hacks" that may have been done on them over the years.Sherlock Holmes time
I've just spent a good couple of weeks sorting out a pal's 1976 Bonneville.Some genius had screwed up the charging system and I had to work backwards to find the faults.Never assume anything is right and get as much info from the manuals and Google as you can and ask questions.