1993 w140 rear headrest

Do you mean, that head rests will not retract by means of the button?

They are operated through the pneumatic system, which also controls central locking among others. Does central locking, back up assist (small "antennas") etc. work?

Retraction of rear headrests is done by pneumatic unit - the same used also for central locking, trunk lid handle etc.

Are these other things working correctly?

yes im refering to that. central lock works ok,( fuel tank door only opens, not close, had to replace it) back up assist ok, had to reset door assist. any other fuse reset? thanks for your help

Door closing assist works by a separate pneumatic unit, which you reset by a fuse 9 in the trunk fuse box (as your obviously are aware).

Central locking pneumatic unit has power through fuse 11 in the trunk, but I don't know if that helps anything. Try it.

I was just thinking - can your headrests both be raised and lowered electrically, or can the only be retracted from the instrument panel?

And what does then not work?

The electrical heigth adjustment is a different control module, which get power from F15.