69 Custom 20 w/ extra gas tanks

[Gruman]

Here is what I believe is the extra tank selector switch on my C20 custom. The direction its pointing now, I think, is to the tank behind the seat. I have 2 more tanks just behind the cab on each side with the aluminum covers on the outside of the bed. The stickers/writing has worn off of the selector switch and was wondering what direction would the selector have to be in to select the other 2 tanks?

Or... Are the left tank and right tank connected? Are they all 3 connected? What was the usual setup on these?