- Feb 28, 2014
you can only exclude the things that test bad~!!!!!
open the primary and see if the rotor is well centered when you roll the bike over. If the stator plates are rainbow colored that's a sign of overheating from rubbing between the rotor and the stator. SO,... you could be testing and be finding good voltage due to the battery being new, but your Rotor/stator may have over heated due to rubbing and be shorting out intermittently. That would explain the meter going back and forth
This was the situation of my bike when I bought it. The previous owner was charging it, going for rides, and having to truck it back home when the battery ran low. Eventually he wanted to get rid of it because he didn't want to work on the bike or learn, so I got it from him for $500. The rotor plates had that rainbow coloration from overheating due to rubbing from the rotor.
In the case of my bike, a '70 model, I have an ammeter wired into the harness, so I can clearly see if my stator is charging the battery when I'm riding....
But wait! There's more! An ammeter will only tell you how much the output of the alternator is. It cannot tell you how much the battery is being
charged in volts. There is a regulator in-between which transmutes (is that a word?) amps to volts at the battery. Charging at the battery must
be measured at the battery.