I am wiring my boat with a Perko 1/2/ALL switch and I'm connecting the
hot (+) lead from my accessory panel to the COMMON termial of the
switch (this is the same terminal that runs to the engine as well).

My question is this: Does it matter which battery I connect the
ground (-) to. Seems like a dumb question, I guess, since both
battery grounds are conncected together, but I thought I'd ask anyway
just to be sure.

Many thanks...