If your RV was built on a Ford cutaway chassis, you can look for the Ford "Body Builders Layout Manual." eBay is one source. Here's a link to one from 1994:
1984 Ford Bronco E F 100 150 250 350 Truck Body Builders Service Manual Book 84 | eBay
Ford has a Body Builders Layout Book Web site:
but that only goes back to 1997. Some things may be similar to your 1985, but others quite different, as by then Ford had shifted over to the V-10 for its cutaways.
There are usually service manuals, including the ever-popular "EVTM
" ("Electrical and Vacuum Troubleshooting Manual"), available on eBay and elsewhere, too.
Where to get the rest of the information, like for the water, non-chassis electrical systems and such, if not covered in the Fleetwood owner's manual? The Web will be your friend.