Some info from drawings that may help to find things?
This drawing and on page 3 has the items you may be looking for currently:
There are a number of the really important things under that seat and I have marked the "big three" as of them is what you may need to find today.
Breakers are always good to know where to find them, then probably the next two are the "battery cutoff relay" which should work with a switch somewhere to cut power to most of the Rv inside things like lights pump, etc. but not all as there are safety items like CO and propane detectors that are left on. Be aware that those small drains can run the coach battery down even when the switch says cutoff!
The "mode solenoid" is a frequent question and is important--- also what you may be involved with today.
The mode solenoid does two things which are the same but done in opposite directions/purposes.
One mode is the boost switch on the dash which sends power to pull this solenoid temporarily while the button is pushed and the solenoid connects coach and start batteries together to "jump start " the engine. Nice if the start battery is low! Power from the coach battery to the start side!
A second mode is when we having the engine running there is power sent to this solenoid, pulls it to connect the batteries again but this is to let the engine alternator charge the coach battery while we drive. Power from start goes to coach!
This solenoid is pretty big and chunky, so if you put a hand on it while hitting the boost switch or while starting the engine, you can often hear and feel it jump!
Click this picture to bring it up bigger to view.