The door latch assembly includes the lock actuator and the door ajar switch. There are four wires going to it:
TAN wire, unlock control voltage
GRY wire, lock control voltage
LT BLU/BLK wire, door ajar switch signal
BLK wire, door ajar switch ground
If you measure the voltage across the TAN and GRY wires, you'll see a positive voltage when unlocking and negative voltage (reverse polarity) when locking. If it turns out to be the actuator, you can replace the whole assembly or leave it in place and then graft on a universal actuator (dime a dozen on eBay).