E46CT

I did this to my CT200H F Sport... but you guys get the idea. I imagine something similar could be done to the 3IS. I could be wrong though. You would have to locate the wire responsible for signaling to the camera to turn on. (assuming that's how the system works in the IS) Maybe someone can look into it if bored.

I did it for fun and always wanted to turn the camera on at will. For the CT, I had to play around with the multimeter to find out what wires did what. Found a 7V feed (strange voltage) that gets activated by putting the car in reverse. I located the two wires and jumped them using a piece of wire. And voila the camera sure enough turned on. So just installed one of these switches and ran some wire to the switch spot. I ran it for a while, I don't notice it getting warm at all. i'll monitor it closely to be sure. Tiny screen though so it shouldn't be a big deal.

My ultimate goal would be to activate the rear camera when the turn signal is activated. But I would need to find a way to provide constant voltage when the turn signal is activated... perhaps by a relay and capacitor. But i'm not too good at custom electronics like that so I'll have to do some research. Cars like the Honda Fit come with this factory for a while now and it would be nice to take advantage of the 3IS's large screen to see behind you when changing lanes.

E46CT

Update I tested it more, do not do this. When it turned night time, I saw my reverse light light up. Didn't notice it in the bright sun when I was doing this. Apparently I would need to split the circuit with two relays. Without it, the backup lights get power whenever the camera gets power because they are on the same line. Too much work.

It's fine anyway the screen is distracting with having a half mirror as on the CT. So I'll look into another option involving a separate screen i can perhaps mount down low and maybe surround view cameras. There's kits on eBay. I want my cameras!! Tesla style. Or at least a front camera.

apparently i created the worlds coolest anti-tail gating feature. and thankfully it doesn't throw the car in reverse.. lol. i'll keep it wired for now.

itsx

For a non-diy route, the Beatsonic front camera kit gives you a button that'll give you the feed of the front view camera, tap it again it'll switch to the rearview camera. it's on a timer so it'll return to the regular radio screen. It will behave as if you put the car into reverse, like it'll overlay on top of whatever you have going. But the beatsonic route isn't as budget friendly than your setup.

E46CT

I would probably do that if i kept my 3IS. i will look into some other camera options and a mini screen. Someone did a cool custom screen mount (very simple one) in the CT section. My particular car does not have the nav option so no natural screen for me.