I'm just having a look at the wiring diagram for the car, but sadly it doesn't seem give the wiring colour codes for any of the central locking wiring.
There appear to be 6 connections to the passenger central locking. One is a 12v supply off fuse 7, which supplies all 3 central locking actuators (4 on cars with a locking fuel flap). 3 wires go across to the driver's side actuator, and 2 of these also connect to the boot actuator - all 3 also go to the central control unit. The other two connections go directly to the central control unit. The actuator appears to contain a pair of switches that swap the direction the motor is driven in - giving lock and unlock actions.
There also appears to be an additional switch in just the drivers side door lock. There does not appear to be a corresponding switch on the passenger side - and I know on my car, there isn't a lock to attach it to!
I think the mechanism is that the switch it operated by the door lock pin - so that when you press it by hand it operates the central locking - this delivers a lock/unlock signal to the control unit. The motor drive appears to be from the three wires that go to the driver's side actuator and the two that go to the boot, so all the lock motors will receive the same supply for the same length of time when they operate. This tells me that a short in any of these three would stop all the central locking actuators from working, but a clean break would stop either all three, just the drivers side, just passenger and boot, just passenger, or just boot. The supply does not directly drive the motor, so I wouldn't advise my earlier suggestion of trying to apply a voltage to it to test it - it may very well not be 12V.
There is a link to the download page for the circuit diagrams in the knowledgebase - BMW call them the ETM (Electrical Troubleshooting Manual).