I just removed my old 55 amp Mando alternator and installed a single wire 135 amp alternator. With the Mando I know it was not advisable to switch the battery switch with the engine running. Something about a field disconnect. The single wire alternator has a 4 gauge wire to the common on the battery switch. The switch is a Perko 1 ALL 2 style with the posts on the switch for field disconnect and is advertised as a make before break type. I would like to be able to start on a good battery and then switch to the near dead one while running. In the past I would start on ALL if #2 was very low and let it charge for a few minutes then shut it down and go to #2 once it had enough charge to crank. If the switch is a make before break it seems I could start on 1 or ALL and then move to #2 without shutting it off. Will a single wire alternator allow this without damaging something?

Intresting question. I didn't know about not switching batteries with the engine running.

As long as the batt switch is the "make before break" type you can.
It's the type of switch that when swtiching from one batt to the other will briefly connect both batt's together before it disconnects the first batt.
If it isn't this type you'll fry the diodes in the aternator.

I suppose the only way to know for sure would be to ohm the switch out.
Payton, also depends upon the type of alternator you have. Many of the Prestolites need a battery switch with a field disconnect. Check with someone who really knows. You can toast your alternator if you don't have the correct type of switch and wire it properly.