

E D I T: click for bigger pics.
Fwiw, to get the tailgate to lock with the central locking we had to make sure the tailgate lock (keyhole bit) is all the way to the left (it's a three stage lock: all the way to the left = central locking, vertical-ish = locked by the key, all the way to the right = unlocked by the key).
Here's a video that might help to see how the central locking system works (vid shows it unlocked, then locked, then unlocked again).
