Not only Ampico uprights have bad wiring -- Duo Arts may be included.
I posted a couple of years ago a message about my Weber 5'8' 1926 era.
The metal-jacketed wiring (Romex?) felt warm after playing the piano for
15 minutes. I was feeling the new switch I'd installed, to make sure it
wasn't overheating. I happened to run my fingers down the line and
noticed that the wiring was warm. Fearing insufficient current to the
motor, I dissected the wiring the next day.
Sure enough, the stranded copper wire had turned green, and was moist
and pasty and slightly grainy. My guess is that sulfur from the rubber
coating had combined with the copper to produce copper sulfate (a blue-
green, highly toxic substance -- don't eat it). I left the piano un-
plugged while I searched for original type wire, but had to settle for
aluminum flex conduit.
I wonder if anyone else has noted this, or was the 1926 wiring I got just
a bad batch.
[ I recall that one of our MMD chemists explained that sulfur is a
[ primary constituent of rubber, therefore "if it looks like sulfate,
[ it must be sulfate." I, too, have seen old rubber-insulated wire
[ which looked like it had baked in auto-battery fumes! -- Robbie