If you could post a pic of the mystery item and it's surrounds we can give a good guestimate..........battery switch is usually in close proximity to the Setec usually similar to a light switch but then the water pump switch can be as well.
Battery switch is near fridge and solar panel junction box. Water pump switch is next to the door and part of the battery level and tank level switch system. Hot water switch is usually next to setec mine is at floor level.
Your switch seems to be related to sound system..
I do know that switch positions can vary significantly depending on whether the person who ordered the van put in special requests. Mine were the default positions as I didn’t know about special requests when I bought mine in 2013.
Photos can help.