For the chassis, you would have to contact the chassis manufacturer. For the body, you would have to contact the body builder. There isn't one universal wiring diagram for all school buses.
http://www.vintagebus.com/wiring/index.html
The bentley manual "green book" has all the wiring diagrams you need.
MC truck and bus Maidstone will normally fax over sections of Volvo wiring diagrams on request
go to http://www.thesamba.com/vw/archives/info/wiringt2.php you will find it there
Call your local Bus Barn or the Unified School District. They will have information if there is a recently retired school bus. Be sure to find out why the bus was originally taken out of commission before making your purchase.
google imagesGo to this web site: http://www.vintagebus.com/wiring/index.htmlIt has wiring diagrams for Bus, Beetle, Super Beetle, Karmann Ghia, Type 3, Type 4, Type 181 (Thing), Type 48 and Kubelwagen. Years ranging from 1950 - 1991.
Find a school bus matron training for a two week class
There is usually a diagram on the reverse of the fuse box cover. if
The "bus" is the communication system that the computers use. "no bus" means that the system is not working and no communication is happening. A scan tool and a wiring diagram are required to diagnose.
I can help you if you tell me which engine is in it.
usually it says it on the side of your school bus
You can find a cheap school bus for sale on craigslist. You need to do your research and make sure that you are getting a legitimate school bus in decent working condition. You should also bring along a mechanic for inspection.