If you have your engine serial #, you can create an account on Cummins QuickServe Online: https://quickserve.cummins.com/info/index.html
The Engine data plate for ISC should be the same as on ISL on top side of gear housing like in the attached pic.
It's not the easiest site to navigate but once you get used to it, has lots of info including engine diagrams and component locations. The components can also be tricky to find unless you know exactly where to look.
If this coach is new to your, a previous owner may have done conversion from an oil pressure sender to a switch per the attached bulletin.
It does not explain why but we went thru similar move in the automotive industry. Too many complaints from ignorant customers why the oil pressure keeps changing but there were other factors at play also like corroding connectors on the old senders, cost to retool etc.