Re: Batt switch off, engine running, fire!
With no battey connected, the voltage from the alternator will be much higher than 12 volts. That would have damaged the electronics.
I would look at how the engine alternator is connected to the battery. Sounds like its connected to DC Panel. If the alternator is connected directly to the battery, it would not power the DC loads unless the switch was ON and this won't happen again.