Since I can't stand it when people don't tie up their threads...
After tracking down some wiring I discovered an isolator and it's control box hidden discreetly under a dangling coolant overflow tank on the opposite side of the engine bay from the chassis battery. It would manually engage with the boost button in the cab, but the control board wasn't doing its job. I jumped both hot terminals on the isolator solenoid and the house battery started charging just fine. It was 10 pm by then at Lake Tahoe (high end tourist community) and the folks are driving back to Denver. Told them to USE THE FRIGGIN GENERATOR IN THE EVENINGS instead of just killing the house battery. Warned them that they will continue to not charge while driving.
Thanks for all of the input.
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