The alternator feed should be routed directly to a battery bank - or through a diode to several battery banks. Wiring
the alternator output to the common terminal on the main battery switch is rather dangerous to the life of your alternator - especially if you are running the engine
and forgot to put the battery switch in "both" BEFORE starting the engine
. Switching the battery switch with the alternator running can "disconnect" the alternator from its battery "load" resulting in voltage "run-a-way" and failure of the alternator. There are special main battery switches that have a "field" interruptor provision to protect the alternator, but if your main battery switch does not have this feature be sure to move the alternator output cable off the "common" terminal and to one or the other battery cable terminals on the switch.