What part of the door mechanism controls auto lock?

So my 250 drivers door stopped locking recently when setting off in the car, when walking away and when activating with the fob. I've replaced the door lock but it's made no difference. Could it be a fuse or wiring somewhere...or an alarm control unit OR could it be that the rear of the door handle (inside the door) is the thing that disengages the handle pull connection?

Anyone got any ideas?