OK, I looked at my piano and service manuals, and I can give a better
description of the manual loud/soft lever.  The lever is linked
mechanically to a (double pole double throw?) slide switch which
activates either of 2 sets of pneumatics.  The LOUD position activates
the LOUD pneumatic on each side of the piano (bass & treble).  This
pneumatic pushes up at the base of the rod which is normally controlled
by the 1-3-5 tracker bar channels on the Ampico, and forces the piano
to play louder.

By the same token, sliding the lever to the SOFT position moves the
slide switch to activate the SOFT pneumatic for each side of the piano
(bass & treble).  This pneumatic pushes up at the base of another rod
which goes into the box along with the first rod; I don't know exactly
what goes on there but you can imagine.

I didn't find detailed descriptions in any service manuals, but it is
very accurately pictured in a large foldout pictorial parts list of a
Stoddard Ampico upright, almost identicle to mine.  The green-covered
manual I have is for an Ampico A which doesn't have the mechanism we're
discussing.  Neither does the B manual, of course!

BTW, you can buy a bunch of assorted service books from the MUSIC ROLL
SHOP in Rawson, Ohio (419-963-3075).  I believe they bought out the
remaining stock of AMR's piano service books, and they have a full-page
ad in the most recent AMICA bulletin (pg. 220).  I'd recommend getting
any or all of these, as they may be VERY difficult to get after this.
I hope this helps!

Cheers,
Rob DeLand
(deland_robert@macmail1.csg.mot.com)