For lock - unlock, in 1989 models, the only monitored locks are Driver's door and Trunk lid. You can verify it trying to lock all the doors with the passenger's door knob (it is not supposed to work).
If the problem does not show when you operate the trunk lock with the key (to the horizontal position, counter clock wise I think), or the lock does not work, it should be the trunk lock, and then probably the hinge harness (Remember Doogie's issue?).
If the problem does not show when you operate (lock) the driver's lock with the knob, or the lock does not work, it should be the driver's door lock, probably the micro switch inside the actuator.
For unlock - lock, I don't know, my car also has a estrange behavior in which some times when I stop to let a passenger out, and I unlock the doors pulling the knob or the handle, It locks again. Have not debug, nor study this as don't bother me enough!
Javier