Remote Control Replacement Seat Ibiza TDI

Hello!

I drive a Seat Ibiza GT TDI, manufactured in August 1998 (engine code AFN, 110 hp). Since my remote key fob stopped working and the original keys are very expensive, I decided to...
To install a different control unit for the remote central locking system (including a new transmitter). Unfortunately, I don't have a wiring diagram for the original control unit (pinout).
Does anyone have experience with installing this, or a wiring diagram? Also, I have no idea where this component is located (perhaps in the sill?).
The new unit is from WAECO (model MT-350, magic touch).

Best regards,
Thorsten.
javascript:emoticon('')