Lumbar controls W126

Hello,
I've got a set of Merc W126 seats out of a 450 SEC which I will fit into another car. These seats have the lumbar support option which I believe to
be powered by the central locking pump. As I don't have this, can anyone advise me on whether this system is controlled by vacuum as per most central locking systems or by positive pressure? Also, should there be a valve fitted in the system to hold the pressure/vacuum or does the central locking pump take care of this?
Either I can make this work cheaply with a bicycle tyre valve, cheap c/l pump and manual switch or I'll just do without it.
Many thanks.
Mercurious
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