Factory location for second battery/switch- 1992 v20

[Petrus]

Am looking to add a second battery to my 92, from what I can tell, it looks like the second battery would go right next to the first in the rear starboard well.

Any idea where the factory would have originally installed the battery switch? Am thinking it would have also been in the well above the batteries but am not sure where to put it. Transom maybe?

Want to get this right before I start poking holes in the wrong place!