Ah, I understand.That isn't how they work. To operate the lock the 12V and ground wires are attached to the tan and grey wires. One polarity locks, and the reverse polarity unlocks it.
Specifically, 12V to tan and 0V to grey unlocks, while 12V to grey and 0V to tan locks.
The ground in the connector is used for the door ajar switch and has no function with the locking mechanism.
I tested again as you suggested and the driver side actuator works in both directions, lock and unlock when reversing polarity. I will install it back into the car door.
So my problem is not related to the door actuators, but rather elsewhere in the door lock control system. Do you have any clue where to look next?