Drop down the trim at the rear when you open the hatch and you can pull the headlining down enough to remove the connector and then the bolt securing it.
 
Have you got the standard head unit?

No I have a sony one, when I bought the car the amplifier had gone in the headunit, it tuned into stations, played CD's just no sound came out of the speakers!
I had an old sony at home and the fascia and harness was only £7 so cheaper than buying a replacement standard head unit.

To be fair I would rather have a standard one that someone doesnt want really really cheap!!
 
Mines a Kenwood too, want a better one but aont guna hppen for a while. Anyway.

Mines needs the aerial adaptor but might aswell hlget everything at same time.