In reference to the description of the surviving parts of Opus 1409,
the so-called switching mechanism is probably a short, usually
free-standing affair (sometimes mounted under the roll frame of the
wall-mounted installations). This is more than likely the pedal
coupler: it couples the Pedal division to the lowest end of the Great
division holes. This is a very important item.
I hope this is of some help to you, (if I am correct in my assumption),
otherwise, in the words of Emily Litella, "Never-Mind"!