Will do that tonight. Not with the car right now.

If it's 17 pin, is that good news or am I still in the same boat?

As things stand, I know I have a MK3 sat nav unit in the back and I know there is a smaller black box next to it with an aerial feed into it which I am assuming is a radio receiver.

If this unit also feeds the speakers I should be able to see that from the number of wires leaving the unit right? Or am I misunderstanding this i-bus business? It sounds like witch craft!

Thanks again for your help, I've been tearing my hair out trying to understand the current set up.