Some of Onan's early generators using the J1939 Network Interface Module (NIM) used ceramic resonators as opposed to crystal oscillators for the clock or timing source. Since the ceramic resonators are not as accurate or stable as crystal oscillators, NIM boards using ceramic resonators frequently violate J1939 bus timings to the extent that the J2K100 can not interpret J1939 data coming from the generator. If you are absolutely sure that you have everything correctly connected and configured and you still can't get the J2K100 to output any NMEA 2000 information, you may need to contact Onan to see if the NIM boards have ceramic resonators, and if so you, will need to exchange them for NIM boards that use crystal oscillators.