They replaced everything except the wires? Maybe? A 3 conductor wire runs out of the gen, L1, L2, and common. Common goes to the negative of a house battery through a battery equalizer creating a “virtual common” which no one can explain to me. The generator frame ground is to the hull, properly. The negative of the house bank goes to the hull, properly. But if I switch off the battery equalizer, I lose the generator common, improperly, which causes about $8k in damage to sensitive electronics like the air conditioner controllers.
It is probably “virtual” because it is probably not tied directly to ground. When you turn that thing off, you are probably making that common a floating node disconnected from ground.