So I can't sleep, I like reading circuit diagrams, and I'm weird like that... I did some digging in my FSM ('03 Durango) which should be fairly similar if not the same wiring as yours (I know its the same switch and lock actuator at least)...
It is the CTM that the circuit goes through. :banana2:
The lock actuators work based on which direction the power is flowing into them (like a
water wheel). In the drivers door lock actuator it will have an 18 gauge dark blue wire and an 18 gauge orange & black wire going into it. During 'unlock' the dark blue wire should have power and the orange & black wire should have ground. During 'lock' the dark blue wire has ground and the orange and black wire has power. In both cases, power is 12 volts. A more conclusive test that the actuator is working properly would be to swap the wires. Plug the dark blue wire in where the orange & black is, and plug the orange & black where the dark blue wire was. Then try to 'unlock' via the door switch. The drivers door should lock in this case, while the other doors should unlock. Make sure to put the wires back where they were when your done with this test, btw.
If the above test checks out, next test the switch. The switch tells the CTM what position it is in (lock/unlock/neutral) by how much resistance it applies to the CTM's signal. In other words, how many volts/current goes in one side compared to coming out the other. You can test the switch by disconnecting it from the wiring harness and testing pin 7 (20 gauge white & dark green wire) and pin 11 (20 gauge black & light green wire) in connector 1 (the one with 12 pins in it) for resistance in lock/unlock/neutral. It should be 10k ohms, 820 ohms and 320 ohms in neutral, lock and unlock positions respectively (+/- 1%). A good muti-meter should be able to do this easily.
If all that checks out, disconnect each lock actuator one at a time (including the one in the lift gate) and recheck if everything locks/unlocks from the drivers door switch. A shorted lock actuator can throw the entire circuit out of whack since they are all connected, but I would think it would make the circuit completely fail, not fail in only one direction. But stranger things have happened in circuitry.
If all that checks out, I would suspect a short between one of the lock actuators and the CTM (let me know if you need help with that) or in a worst case the CTM may be bad.
btw, do any of the other door lock switches lock/unlock that door or do they only unlock too? What about if you put the key in the drivers door lock and turn it twice in a row in either direction?
Also, you are doing all this with the key
not in the ignition and the headlights off, aren't you? The CTM won't let you lock your keys in your car, or leave the lights on in a locked car that easily. :woot: