I am planning to change the stereo head unit on my 2009 Caddy. Currently I have the original RCD310. I am going to install a single DIN unit so I realise that I need to buy a new fascia due to the difference in size, but will I need a harness adapter or aerial adapter or should I just be able to plug the new unit in to the existing wiring? Halfords sell a complete kit but there is no point in buying it if I just need the plastic facia.

Any help would be appreciated.