I'll have a go at this one.

Pedal On -- when open this connects whichever notes of the bottom 30
on the Accompaniment to the Pedal stops.  But there's more, and herein
lies the genius of the system.  As long as the pedal notes are held,
they remain connected to the pedal stops even when the "Pedal On" hole
is closed, thus allowing the entire compass of the accompaniment to be
used normally, without playing on the pedal stops.

Manual Off -- this works the same as the "Pedal On" except when open
it disconnects any of the bottom 30 Accompaniment notes played from the
Accompaniment stops.  It also keeps those notes disconnected from the
Accompaniment as long as they are held.

When used in combination these two holes permit the effect of an
independent Pedal.

I hope this helps,
Ken Clark