The powers that be want you to buy this stuff however here are links to Onan manuals for your 6.5NH unit from my personal collection:
Operators Manual (940-0121):
https://dave78chieftain.zxq.net/OnanM...20940-0121.pdf
RV Genset Service manual (900-337):
Onan 900-0337 Bf-Bfa-Bga-Nh Service Manul.pdf
RV UN Genset Controls Service Manual (900-0196):
Onan 900-0196 UN Generator & Controls Service Manual.pdf
Collection of Onan Support Info:
https://dave78chieftain.zxq.net/OnanM...hBulletins.pdf
Dave