I just finished up hard wiring my front video camera. I decided to tap into the switched 12 volt and ground that is going into the auto dim mirror (off of the auto wiper sensor). What I needed for my project.

Inexpensive but 5v 2.5 amp cigarette lighter converter. ($4 at Fry's)
Roll of electrical tape.
Red wire taps (the smallest gauge they come in)
1 foot of electrical wire, I used some off of a broken power supply.
Solder
Solder Iron

Dismantle the cigarette adapter. You should be left with a usb plug attached to a circuit board a spring or wire going to the tip and a leaf spring on each side. The spring sides are the ground and the tip is the positive. Solder on about a half a foot of wire to each the positive and half a foot of wire to the negative. Insulate with electrical tape. Insulate the rest from an inch or so down the new wires up and around circuit board and the USB component.

The next part I had to guess, I figured I had a 50 / 50 chance. There were 3 wires, a red a black and a green. I was pretty positive the black was ground and one of the other two were positive constant and the other positive switched. I guessed right, I tapped the red and spliced in the positive of the wire that lead to the USB circuit board.. After that I tapped the black with the other wire leading to the negative of the USB circuit board. I turned on the car and the usb lit up. It turned off when I turned off the car. After this I plugged in a short USB cable wrapped it around a little and put the covers over the rain sensor. I wired the usb cable to the camera.

What is good about this setup is that if the plugs change, as long as they are USB I can just plug in a new cord. If its just looking for 5v I can just convert a USB cord.

Nice. I've been thinking of doing this too, using a camera such as this:

http://www.ebay.com/itm/IROAD-IONE-3800 ... 43bd32268f

Thank you so much for this. I think I'm following what you are saying and I want to do this for my camera as well and this is exactly what I needed. Awesome!

There is a company that makes both a mounting bracket and power cord for installing a radar detector off the rear view mirror. Works fine. I also want to change my rear view mirror to one that has both the outside temp and compass. I will post the company's name for the bracket and power cord.

if youre going to do a how to, pictures will help a lot for people who are visual learners