Yeah, dude, it's MAD easy. There is a big fat power button. In fact, there are two buttons, one for on and one for off. I think the button labeled "I" is for on, and the button labeled "O" is for off. Push the "O" button and the little green light at the bottom of the mirror should turn off, signaling that it's off.
Heh, it's funny that you want the auto-dimming feature turned off, because I wish that our side-view mirrors had the auto-dimming feature.