The place to go for Onan trouble shooting is here:
https://www.smokstak.com/forum/forumdisplay.php?f=1
They also have factory service manuals for your models, which include diagnostic procedures.
I'm in the middle of fighting with my Onan and have been for months. This week I'm pulling the voltage regulator and control board (both Flight Systems replacements replaced in 2009) and sending them in for testing ($35 each which they refund if you buy a new board).
Steve