As noted below (but one might miss it) -- be careful if you have an alternator hooked "putting-out" without a battery connected to it. It would likely blow the diode(s).

That's the reference to a "break" protection discussed below. (I don't think that Greg's switches have that, per se. If you use those, you need to be much more cautious as you switch around).

Depending on the age of your boat, it's not likely (but not impossible) that you don't have that protection on your current switch. You might just check that to be safe. It would an issue if you switched from 1 to 2 through "Both". On some 1 or 2 it is also an issue.

Which controller(s)/alternator(s) do you currently have; and, what is your AC charging situation?

Some people put the engine start on it's own battery without any external charging -- but I've found that surprisingly there are some systems that have a sufficient background electrical use to cause issues with this. Our generator (for some inexplicable reason) has this issue and unless we switch the generator start battery completely "OFF", it will discharge over 4 weeks, or so. "All the King's horses, and all the King's men" haven't been able to figure it out. It's not the bilge pumps.