Jim,
I believe the following is correct, (but I could be mistaken)....... The 'Guest' switch (off/1/both/2) selects which battery feeds the inverter..... I normally leave it set on "both", which, apparently, parallels the 2 house batteries. The two toggle switches at lower left of switch panel are the feed switches for the DC panel.. 1 for house battery 1, 2 for house battery 2... if you switch them both off you have no DC to DC panel... If one of your (4D) house batteries goes bad (as one of mine did), you can switch it off (using its toggle switch) and use the other battery. However, you must also switch off the offending battery w/ the Guest switch. If you discharge your house batteries (at anchor, for example), switch both toggle switches off prior to turning the ignition key "on", to prevent draining your good engine start battery into your discharged house batteries. After engine starts, flip toggle switches back on. Hunter's electrical set-up is pretty confusing; even their service people shake their heads... Anyway, hope this helps. If my understandings are incorrect, hopefully, others will post better info...... Oh, BTW.. not sure what year your 420 is; mine is a 2001 model year built during Aug. 2000. The owners manuel for my boat (as well as, at least, 2 other 420's maunfactured after mine) show a battery isolator being present. It does not exist on my boat or on the 2 others that I have knowledge of... does your boat's manuel show one being present, and if so, is one actually on the boat??
