A connoisseur would probably use a multimeter and measure the resistance between pair of pins when the switch is in one state, then when it's in the other state, and so infer which pin is which.

For the future me, or someone else, who wants a quick answer, here are 1000 words disguised as a picture - black (actually navy blue in the photo) is Ground, red is Power and green is Accessories:

For more information, the guys from http://www.learningaboutelectronics.com/ have a nice article on Rocker Switch Wiring.