There is a tube (vacume line) that runs to each of the locks on your car. Chances are that the tube that goes to your trunk lock is no longer pluged into the trunk lock. If this is so then the question becomes: WHY is it disconnected? Was it done so intentionally for a reason or by accident. If it is disconnected try to plug it back in again and then test to see if the trunk locks and unlocks normally. Tell us what you find out.
1993 190E 2.3
2000 Toyota 4x4 Tundra