You'll need to see if the solenoid is being activated by the relay's action. I had one once that the linkage had been disconnected right at the solenoid (disconnecting the wiring would have produced the same result) apparently to maintain the security of the trunk while the doors were unlocked.

If the wiring and the linkage is in place and it isn't working you'll need to see if you are in fact getting voltage to the solenoid. Voltage and no action would point to the solenoid. No voltage would mean moving to the relay (located behind the ashtray- I forget its exact location but having someone lock/unlock the central locking would produce enough change in the relay that you could feel the movement in the relay case).

Randy