Congrats on the bus.
1) Call the current manufacturer and see if they can help. Some posters have luck with this.
2) Find your electrical panel and see if there is a schematic posted around it. On the bigger buses with the panel door under the drivers windows, they have a full schematic posted on the inside of the door.
3) Buy something like this, https://www.lowes.com/pd/Fluke-Netwo...E&gclsrc=aw.ds
, to trace things on your own. Slow and painful, but without any other guidance, it's a way to identify what goes where. It will come in handy down the road anyway, so good to have.
4) There are sites that sell manuals. I'd search on those and see if you can find one. It may cost you a bit, but that's all part of the cost of conversion.
Hope some of this helps.