Welcome to iRV2 . and the vintage Newmar family .
Could you add chassis info to your post ? Freightliner or Spartan ?
Newmar had many options back in the day , does you coach have a single , converter/charger in the power cable bay , or two ?
Or do you have the optional 2000 watt inverter ?
2 or 4 coach batteries ?
There is only a single breaker on my 7500 gen set , I'd imagine yours is the same . But it might be worth the time to cycle the switch fully off and on .
Then as twinboat mentioned , it's time to start testing genset power to all the 120 volt outlets in the coach .
Somehow the converter /charger isn't charging the batteries when gen set is running.
Is your Power transfer switch the original " Todd Engineering " as shown in this picture of my power cable bay .
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.