I have a pedal electric Duo-Art in an upright Weber, and during its
restoration I encountered the pump motor on-off switch.  I am not
surprised you got a shock from it, Steve, as these switches are not
designed with electrical safety in mind.  But the problem I faced
was finding a safer replacement, which turned out to be impossible.

The toggle action in the original switch is less positive than in
a typical switch of today.  Replacing the switch would therefore
mean the new switch would be difficult for the pneumatic to operate.
So it came down to insulating the original switch in some way.

In my piano, the switch is attached to the treble side of the inside
case, with its toggle linked to a metal rod with a brass knob on the
end.  The rod extends from the switch to the spool box.  Pull the
brass knob and the pump motor turns on.  My observations of the switch
showed that the toggle component in the switch could easily contact the
metal cover and the metal toggle.  I did what I could to remedy that,
but one has to be careful to not damage or upset the toggle action.

I then made up an insulated link between the switch toggle and the
metal rod.  This makes sure the rod and its lovely brass knob can
never become live.  As for the switch, while I know it's ok, I regard
it as hazardous.  That is, the metal cover and toggle can become live.
Because it is mounted well away from everything, I decided to leave it
as is, but to check the situation with a voltage indicator probe when
ever I was working near the switch.

If others are likely to work on the piano, e.g., a piano tuner, it is
probably best to build a cover over the switch.  However I prefer to
be able to easily check the condition of the switch, in particular how
clean the contacts are.  Dirty or poor contacts can cause the switch
to become hot, and possibly cause heat damage.  Covering the switch
could therefore prevent you noticing it getting hot.  On the other
hand, it is unlikely heat will occur, as the contacts in the switch
seem to mate well enough.

So it's a case of doing what you can, and taking the attitude that the
electrical installation in a player piano is hazardous.  Hope this
information helps.

Peter Phillips
Sydney
http://www.petersmidi.com/