Ok fairly common problem with the rear left door lock. Door will lock with the key but will not unlock using the key. Simple problem with the locking Mech which you have to replace. A motor burns out apparently. So new lock purchased and today I took on the fiddly job of replacing the old lock with the new one. Boy is it a fiddly job. New lock in and door reassembled and I now have a door which will open on the key but......................................
Now the bloody thing will not lock on the key not just this door but the whole car. What is happening now is the door is not registering as closed so the central locking will not lock on the key. On the dash the warning light comes on to say the rear door is still open even though it has been slammed shut. You can manually lock the rear door from the inside and it is locked on the outside, then you can open it with the key but because the car is not registering the door as closed it will not lock any of the doors with the key you just get the warning beep.
Have I done something wrong?
Getting frustrated now and might have to put the old lock back in just so I can secure the car for the night.

 

I think you will find something not fitted correctly on the lock. I seem to recall something on one of the forums saying the same thing!

 

Thanks John but I now think the problem is solved but don't ask me for an explanation.
I drove the car out to pick the wife up from work and noticed the internal light was on. The reading on the dash was still telling me the door was open. I tapped the internal light to switch it off and the warning light on the dash went off. Stopped the car and locked it on the key and it worked perfectly. All the doors lock and unlock as before.
I hate modern electronics. There is no rhyme nor reason sometimes it is just witch craft. Someone would have charged me £100 to switch the internal light out.