the factory locking uses a long rod attached to the boot lock, which is actuated by a vacuum servo like the rest of the locks. the manual lock button is completly different so isnt going to work. The central locking lock also has 3 positions rather than 2, 'always locked', 'always open' and 'central locking'
I have converted mine to aftermarket central locking without much bother, i took a factory central locking lock and mechanism, and bodged an electric servo to it. hardest part was running the wires thru the tailgate, but not that bad. Done my petrol flap too
