Dicky central locking....

[scooter perv]

Sorry for all the questions but gotta iron out a few problems of which I would like sum advice if poss 

 When I went to buy the car (`90 gti 8v 5 door)  I asked the guy if it had central locking and he said it didnt but was sure it should have...Anyway got it home and a few days later when locking driver door the central locking clicked in and locked all doors..Tried it a few times and it worked ok..Missus went out with the spare key and it refused to work for that  Now it refuses to work again with either key and also when you try to lock passenger door it springs all the locks open, and likewise when you go to unluck passenger door the lock flicks open then locks again withing seconds..bit worrying that we may get locked out at some point 
 Any pointers from the experts on which sort of direction I should point the screwdriver?

[GTXcess]

First thing to try is take the drivers door card off and locate the actuator switch (generally blue) which is connected by a rod to the door lock and lock plunger (black bit on top of door card for locking and unlocking doors).  This solved the problem on mine as water had got inside the electrical connection and if yours has a life of its own is the first place to start.

[scooter perv]

thanks matey..shall take it apart now I know where to start 

[rubjonny]

sounds like a dodgy aftermarket kit, the factory system only works from the drivers door.  Check the boot on the passenger side, if you find a big foam box with a pump inside then it had a factory system at some point.  Central locking was never standard on MK2s either