New MH - battery drain question

I remember coming into the coach sometime in the last year and finding no 12v where I expected. First stop was panic, "Now What!" next was some trouble shooting as suggested in my first post. Finally I remembered there is a 12v on off switch called a "Salesman's Switch" by the door. It has no use to me as one who lives on his coach. It cuts off a lot of 12v - lights and refrigerator mostly so when a salesman leaves the coach on the lot he doesn't have to go through and find all the light switches to turn them off to save the battery for the next walk through. Still don't know how it got turned off.