BMW Repair: 1985 318i bmw, master lock, bmw

Question
where is the (I think is called) the control for the central locking system?  Our master lock on the car isn't working and we can't find the controller to replace it or fix it.

Answer
The control unit is located behind the left front speaker.Remove the speaker and the control unit is right there.Many times what happens is the solder sonnection in the control melts down due to too many lock/unlock tries and the solder melts. The cover can be taken off and the connection restored with again solder.