As stated above, there are no electrical schematics for Montanas. But many here have figured out how most rigs are wired. Water heaters are pretty simple devices in the scheme of things. You had a gas/electric one and most likely a Suburban manufactured one.
There are several manuals for the Suburban water heater in the Files section (look in the second, thin, brown ribbon near the top of the page). Here are two that should help.
Suburban water heater service and repair -
https://www.montanaowners.com/forums...?do=file&id=56
Suburban water heater troubleshooting -
https://www.montanaowners.com/forums...?do=file&id=57