There is a water heater manual in the files section
https://www.montanaowners.com/forums...hp?do=cat&id=3
I don't know what model you have if you even have the option to run it in electric mode. If you do, electric mode is very simple and easy to troubleshoot.
The wiring diagram is on page 11.
Make sure the outside switch is on and press both reset buttons. Then try the inside switch again. If you have helper, let them turn on the inside switch while you listen for the igniter to click.
Some older models have a pilot light that must be lit manually before it will operate.
The manual walks you through those steps if that is necessary.