InCar Express wrote:

It seems that some form of adaptor is needed.

By the sounds of things, you don't need anything to connect to the
car, which should have standard ISO connectors. You will however need
the original wiring harness for the Sony unit, which I'd suspect is
missing.

Thanks for that, Jon - now I've got some idea what we need. Not knowing how old the Sony is, can I impose
further on your help and ask whether you have any idea where I can get such a harness? would Sony still sell
them or do we need to look secondhand?

Thanks again,
Marc