Simple one or ther other setup: SPDT Relay...
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I would leave the starter and radio memory wire connected directly to battery. That would leave ALL other power drains, including headlights to be switchable.
One other thing to consider is the Fuel pump, although it is a drain, I'm not sure how well that motor reacts to less than normal 13.6ish volts, at say, 12.5v of a deepcycle under load, that's more amperage, and more heat for that little pump.
I'm starting to think my personal perferece for this mod would be instead of diverting everything, to divert the 2 biggest culprets, Lights, Blower and Electric Fan.
With anything else, there is give and take.
In the winter my commute is in the dark (and cold) both ways. Diverting those 2 loads could be a noticble difference in mileage, while not affecting mission critical devices.