We have one in with same fault but on n.s.r door.
as said it is broken wires on door loom through rubber ducting, this one also needs the actual door loom.
Interesting side effect though, the customer said the radio will only work after actuating the main switch for locking all doors on dash.
All now working after repair kit and door loom fitted, all available from GM, expensive though.
Repair kit retails at £99.50 and door loom is £53.50, all plus vat.
Andy