well from what i remember of the standard central locking (this is me trying to remember something i did over 2 years ago mind!)

4 wires...

1 constant live
1 constant earth
1 live when locked, earth when unlocked
1 earthed when locked, live when unlocked

dunno if that helps you at all

most aftermark systems pulse a wire to lock/unlock and dont keep it live/earth like the standard setup... so you may struggle to get it workin