Both my door locks were not working on my 1992 Ranger but both switches and door lock motors had 12+ volts going to them when the switch was pressed up or down. I got new Dorman door lock motors and we installed the driver's side door lock actuator today. I checked and made sure it worked when plugged in before installing it and it did. Then when we got everything hooked back up properly the door lock would move a little up and down but never push the door lock **** all the way up and never would pull it down in the lock position. The actuator is working though. It's almost like it's not powerful enough. What could it be? The new actuators came with different rods we chose the longest S shaped rod, then there was one a little shorter and then a lot shorter, the other two weren't the same style. Did we use the wrong rod?

 

Two things come to mind. Possible reversing the two power leads and putting the motor in place 'out of phase'. I have seen the motors want to lock when they should be un-locking if the +/- are reversed. I have seen motors strain in both directions when they are installed with the motor arm recessed and the lock button up or the motor extended with the lock button down.
I would disconnect the motor from the lock mechanism and operate the motor using the door panel switch. See that it extends and retracts properly, and then make sure it matches the position of the lock when you clamp it to the lock rod.
You can also check the motor for having enough 'torque' to move the lock rod by moving the rod by hand. If difficult, check for binding mechanism.
tom