This Isolator is an automatic one.
Positive leads of both batteries and a lead
from the alternator is all that it needs.
It will automatically decide which battery
needs charging so the weakest gets the alternator's full capacity. This unit
will also separate the batteries so that if
you are running accessories only one battery
will be used saving the fully charged battery for
starting. My favorite thing about this is it eliminates mistakes made by the operator. I can't
tell you how many times I left my manual switch
on two batteries wanting them both to charge
while the engine was running, only to run them
both down with the radio because I forgot to change back to a single battery. http://ww2.boatus-store.com/images/full/224025.jpg