1994 Firan "Europremier" chassis wiring diagram? New owner

I think you probably replaced the house batteries, but not the chassis batteries. The generator is commonly (though not always) started from the house batteries--and, of course, the various interior lights and appliances and such operate off of them, excepting those directly associated with the vehicle chassis (i.e. the defroster fan, maybe a dome light, sometimes the dash radio, etc.)