This just started a couple days ago on my OBS.. After startup, immediately the voltage needle starts jumping then is stops after a few minutes.. Anyone run into this?

 

Check brushes. May just need a new set. What style Alternator? 2G or 3G?

 

Normally, erratic behavior is an early sign of a failing alternator (diode failure for example).........but it also may be belts, int or ext reg, wiring, battery condition, etc........best to work the simple maintenance fixes first (tighten belts, clean battery terminals/cables, etc)...

 

Not sure..how can I tell?

 

That's what I figured, my first thought was the alternator but I was not sure of any other controlling units. I'll run thought the normal stuff under the hood to see what I find.

 

You can do a quick check of the alternator's internals if your DVM has a Diode Check function..........