LSDsnr
Not a bad work car!
The speaker cables for the rear channels are in the plug that goes into the stereo. Just pull off the drivers side of the centre console and you'll see plugs going into the stereo. Not sure where they run to but i know they are there atleast.
Wiring colours (in the black plug above the white one):
Rear Left (+) - Brown
Rear Left (-) - Yellow/Red
Rear Right (+) – Dark Blue
Rear Right (-) – Light Blue
Thanks for the heads up holden boy! I'll be pulling mine apart over the weekend and I'll try and get some photos.