After doing a lot of searching online for wiring diagrams, I found a bunch of useful info for these buses. The main site I found info on was this:
Index of /tbb
It is a fairly weird site, as it shows up on Google as a site where you'd find dogs or something. But this page has PDFs of all aspects of the bus, wiring diagrams, repair manuals, for front and rear engined MVP buses. So you can download PDFs of it there, but I compiled a collection of docs from here and elsewhere specific to the MVP-ER buses with the CAT 3126b engine and Allison MD3060 trans (all Montgomery county MD buses are this and I know there are a number of these on this site).
Link to the docs I have:
Wiring Schematics for everything, including CAT engine
Front and Rear Axle servicing procedures
Front and Rear Suspension servicing procedures
General service intervals and specifications
Air Brake service procedures and general info
Steering system info and maintenance
Allison WTEC III transmission service, troubleshooting and operating manuals
Older and newer Allison 3000 and 4000 series manuals
It isn't excellently organized, but it is a bit more straightforward. The notagz link also has dozens of PDFs of recall and TSB info for various bus models. I didn't include these in my documents.
Let me know if you need any additional info or documents, or have some that I left out!