Just figure out what wire does what...
orange & green - splice into rear speaker
orange & black - splice into rear speaker
blue & red - pin 2 in audio iso harness
Blue & yellow - pin 1 in audio iso harness
Black - earth - locate nearest earth, probably rear light cluster
Grey - auto antenna, pin 5 in power iso harness
Red & white - Power - splice into igintion switched wire in power iso, or into main power cable,
need to figure this one out as ignition power wire is only on 7.5a fuse, would that blow with draw of sub?
for anyone interested, here is the wiring diagram for the audio system
cropped from a wiring diagram pdf, think its from punto chops or something along those lines
hi res so you can zoom to read easier