For all your camera installations in Sydney, contact this guy. Better than the standard Toyota stuff. Couldn't be happier with his help!!!
http://www.samobile.com.au/As for the wiring of the harness kit.
Most of it is plug and play. Just the green wire with splice crimp needs to go to the red wire with white trace (reverse sense) which is under the passenger seat. The purple wire is the speed sense for the NAV unit. For the colour screen units - I cut the purple so I can use my phone and Ipod while driving....
If you are using an evilbay camera. Buy the harness from Toyota. Solder on a RCA plug for your camera, the yellow video wire to the centre and the white is the -ve shield (there is a 4 pin plug on the harness - white,yellow,black,red), you also need to cut the black wire from here and earth it. Most cameras from ebay are 12V so run the power for your camera to the reversing lights and splice in. The power from the stereo/harness is 6V.
Goodluck!