Methinks you are trying to find a complicated answer to a simple question.
Anything related to portable power is sensitive. It is not plug-and-play.
I remember our professor standing on the dais, birch pointer raised. We had filed into the room 10 minutes earlier and did not know him from Adam.
"Electrical engineering is a DISCIPLINE!" he shouted "Anyone of you who thinks it isn't can gather your books and get the hell out of my classroom!"
Truer words were never spoken. Nothing can be assumed, or surmised. It is done with hard core numbers and calculations. Gut hunches are followed by testing and verification.
Many of the posts I read on this forum grasp at straws. Taking the time to learn the basics of RV electrical is indeed a "discipline". So is parting with fifty dollars or so for a meter and a test light. The reward for learning is the saving of a trip to a mechanic who in fact probably knows less about what you're trying to do than you do. At a hundred dollar an hour fee.
I glanced through a book I believe was titled "The 12 Volt Doctor". I would recommend purchasing such a learning tool. There are others I am sure that are its equal perhaps even better...