red/white - power from fuse box
brown - earth
brown/red - ignition feed
black - aerial and booster (whatever they are)
white/yellow and grey/blue are to do with the lighting. you won't need these for an after market headunit
black/blue - Left front speaker
blue/brown - left front speaker
red/white - right front speaker
brown/white - right front speaker
blue/green - right rear speaker
brown/red - right rear speaker
brown/black - left rear speaker
red/green - left rear speaker
hope that helps
