Door Lock Actuator

[70-71-72]

We were having a problem with our 2003 Buick Rendezvous (I know,... not a real truck) that all of our doors would lock but the two right doors and the rear left door wouldn't unlock. After taking all of the door panels off we discovered that if we unplugged the right rear door lock actuator that the others would start working. Upon further investigation, we discovered that we could get all of them to work if we unplugged the top plug on the actuator and plug the power back in. The change we've made doesn't seem to make any difference but I'm sure it did something. We do have child safety switches on both rear doors that prevent the kids from opening their own doors from the inside but that function seems to be unaffected too. What does this top plug do? What else might it effect by leaving this unplugged?