Generator PROBABLY pulls from the Rear Tank. Given that it does, tank needs to have 1/4 or more gas in it. Idea is to prevent the genset from being able to run the tank so low you can't get off the campsite for more gas.
I think you're gonna have to try and trace the genset fuel line. I added a genset to one that had an '83 E350 chassis and was able to get limited info from the coach builder. Tech there said that an OEM install would pull from a dedicated connection in the tank. BUT if the coach had no genset but was "prepped" for one, that included only wiring, NOT the fuel line. Big help...
In my case, I tapped into the feed line, just before the Tank Select Valve, for the Rear Tank.
Your Chassis Year could be 1984 or 1985 if you have a "1985 RV" so have you looked at Chassis Manufacture Date in the Door Frame? I really hope this isn't a Fuel Tank(s)/Fuel Pump/Tank Select issue. Those can be messy. Pumps aren't cheap and dropping a tank is a pain, but the Select setup with all its wiring and relays gets confusing.
This diagram might match yours.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB