How DOES this actuator work(central locking system w126)

[RG5384]

I have an 83 300SD, and the locking system stopped working very suddenly. I checked the pump with an external 12v battery and it was working, so i then plugged it back in. When i plugged the pump back in it proceeded to run by itself for a couple minutes. I then took the actuator out of the drivers door and disconnected it. next i locked all doors except drivers and put the yellow and red wires together, all the doors opened. I then locked all the doors againa and put blue and red together, again, they all opened! what am i missing here? is there a special switch INSIDE the actuator or is there another valve somewhere? this is puzzling me, i appreciate your help
Ryan