Is your van a "vanilla" Sprinter, or was it factory converted into a camper by someone? e.g. Roadtrek
The answers to questions about class b van campers are often make and model specific, so provide as much of that info as possible, if possible. Someone with your type of RV may have had a similar issue and may know the answer.
Welcome aboard, btw.
Not going to ask about the reversed battery connections.