You sure about that? Sounds like you might have one extra position, or maybe its a newer design switch. Any of the switches for inboards that I have used are like this:
All the way to the left, off. One notch to the right, ignition is on, gauges come on. One more notch to the right, engages the starter. Usually on most small boats, all the accessories (ie bilge, blower, radio, etc) including the trim will work with the ignition off. That's why you have to remember to turn off the radio, GPS unit or else you run down the battery.
The accessory position is not necessary on most small boats because of how its wired like I said above. One click to the right turns the ignition circuit and the engine gauges on, but all your other accessories will work with the key OFF....
However, after looking around I see that there are 4 position switches, with an accessory postion, look here....Not sure if this is what you have, but check anyway.
http://www.westmarine.com/buy/cole-hers ... 75_001_005If everything (accessories) always work regardless, maybe they installed a 4 position switch on a boat that only needs a 3 position one!