I put a volt gauge on my zuk and when the gauge showed a no charge or reading around just 12 it was always because the belt wasn't tight enuff. some how the belt would loosen up on me over a peiod of time. so I would have to adjust the tension on the alt. hoe that helps.
p.s. I had a 88 1/2 brand new back then for about 10 yrs and a took that thing apart from front to back. what a great machine those were. I sure do miss mine. it had a 4 inch calmini lift with 33' tires and a header with no cat. funny thing now is my bro just bought a 88 off ebay that has only 9000 miles on it. jealous lol