[flybouy]

Welcome. Let's see if we can "unpack" some of this as I'm confused (not unusual for me). Your post seems to go in several directions so a few questions.

Are you plugged into shore power? Is this new camper new to you or new as in a 2020 model? Speaking of model, what model is your camper? What amperage is the fuse you reference? You said "did have 2 batteries" connected, still connected? Do you have a battery disconnect switch and is it turned on?

"experimenting" or "playing" with the playing with the slides is not a good idea, especially if the battery(s) are not connected or fully charged. The bathroom "toggle" switch (I assume you mean the rocker style switch) should only operate the bathroom light or fan and not the bedroom lights.

Last question. When you purchased this camper did anyone go over the operation of the systems with you?