Everyone,
It's definitely the Red wire with the yellow stripe. (at least it is on the 2008 GT). You can get to it by removing the kick panel on the right side. There's a bundle of wires coming down from the blue connector - they are wrapped by black electrical tape. Unwrap the tape and sift thru the wires to get to the Red w/yellow one.
I've attached a few photos below.
All in all, the rear camera install is quite easy. I've placed my camera on the inside and at the top of the rear window. (Snaking a wire down the rear door to get it mounted on the license plate seemed like too big of a pain). Snaking the wire from the camera up to the dash was a snap (I went from the rear door to the ceiling of the D-pillar, along the ceiling between the d-pillar and the c-pillar, down the c-pillar, under the trim below the sliding door, under the trim under the passenger front door, and up into the rear of the dash... all in about 5 minutes)
Hope this helps.