And my alternator has
survived since 1991 with a Guest 1/2/off switch.

My understanding is that what can kill an alternator is if the Alt
is putting out power and you switch from, say, #1 to #2. At that
moment when you switch there is no battery connected to the
charging system to take the power thus creating a momentary
surge in power. Some switches are "make-before-break" so
they make the connection to the #2 battery BEFORE breaking
the connections to the #1. (or whichever way you are switching).

But these better type switches can look exactly like the cheaper
type. You have to check the part number (or study it's design
and operation) to determine which type you have.