Okay, so no reply.
I took the front door card off, found the colours of the wires, traced them back to a connector in the boot on the right hand side.
Cut the connector off (blew the radio fuse in the process).
Then, (now with the battery disconnected) I put a 9 volt battery across the (thin, no voltage) wires to buzz out the speakers and identify which were which. Put in an 8 connector "chocolate box" and ran an 8 core wire to the head unit.
I didn't bother with an ariel extender becaue nowadays you can stream the radio.
Works a treat
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300,000 miles and back on the road
Jobs done: Everything you can possibly imagine ... I have the "Triggers Broom" of cars.