That looks like a proper adapter.
There are 2 silver male connectors that plug into the cars existing loom.
Find the one that has the wires that go to the white connector of the BM54.
This is the CDC connection.
I think it has 5 wires connected to it.
These wires are clustered on adjacent pins.
Make sure that they match one to one with the wires in the existing[old] loom.
That should do it, provided the CDC worked with the BM24 or Rover radio.
For the long wire that seems to goes nowhere, check to which pins it connects to on the BM54 connector.
That will give a clue of its purpose.
Have a look at this link to find the pin assignments for the BM54.
http://www.auto-treff.com/bmw/vb/sho...threadid=97606
Hans