Try and disconnect the battery. My 1988 300E was doing the same thing but with the drivers door. You could unlock the drivers door and the rest of the lock would do nothing. I pulled everything apart before I found on this forum, that you can reset the system by disconnecting the motor for the power locks. I just pulled off the negative battery terminal for about a minute, and they work perfect. Unfortunately for me, I had pulled apart half the car before trying this.