I have the same problem with my 1983 380 SEL. As Jim has stated it has to do with locking the doors. If I lock my doors the trunk is also locked and I cannot get in with the master key. If I unlock the doors, the trunk is also unlocked. There may be a certain way to unlock the trunk with the doors locked, but I have not found it. At least the frustration is gone after understanding why it will not open.