You most likely have a 454 Chevy engine, ,it is also possible it is a 403 Oldsmobile, as 1978 was a transition year. Either way, firing order is the same:18436572
I have a 78. I discovered on mine that there is a plug in the wiring compartment where the shore power cable is. If the cable is not plugged into the invertor,,the inside lights don't work. Remember, your inside lights are 12V, so they run through the invertor to get power from either the generator or shore power.
Also, on mine, there is a battery cutoff switch in the back compartment on the right side, where the house battery is, , if that is off, no power from the house battery.
I hope this helps\