We have a 96 Flair and upgraded the original converter with an Intelitech multi-stage charge profile.
https://www.amazon.com/Progressive-D...53278941&psc=1 It made a drastic difference in how long it took to recharge our batteries, off grid. We highly recommend one.
We also upgraded our rig from 30A to 50A. You probably will not need to do such a drastic change, as I'm sure only have one roof mounted A/C. We have two, and kind of needed the upgrade.
If you are not boon docking extensively, and if you have 4KW generator on-board you are good. We still have our 2x 6V batteries. We are planning on doing a lithium and solar upgrade, as we want to extend our boon docking from 3-days to 2 weeks or more.
In regard to the previous owners (monkeying) with the 120 AC and 12 DC wiring, and associated systems.... So sorry to hear that, but glad Fleetwood gave you the basic wire schematics. Have heard from others (recently) that Fleetwood is not doing that courtesy for old customers any longer.
The good news is running new Romex is tedious, but doable. Also good news is Fleetwood did a good job of making the rigs repairable. Good success and post some pictures of your work.