Dave,
  There could be any number of problems you are having with the rear door
locks. The first thing you need to do is make a determination as the whether
the problem is indeed electrical or whether it is mechanical. The
mechanicals on these cars WILL interfere with the operation of the locks.
How tightly the door closes will determine whether the door will unlock or
even open.
   If I were facing this situation, I would take the panels off of both
rear doors and disconnect the electrical connector located at the bottom of
the door. I would then make sure the two fronts operate OK. From this
starting point, I would plug in one of the rear solenoids. If it does not
work, try to see why by looking into the now open door panel.  It may simply
be a matter of lubricating the mechanisms.
   If  you still can not get the lock to operate, you are faced with the
choice as to whether you want to pull the solenoid from the door.  If you
can get to the linkage, you can see if the solenoid is operating under no
load.  If you can not, the removal of the lock mechanism is a tedious one
involving the lifting of the window frame in order to remove the entire
assembly.
   At this point, I suggest you obtain a Haynes.  Solenoids can be replaced
by aftermarket units for about $10 each.

Cheers
Webserve