One is a 1928 Singer model 66 with an electric motor.

The other is a casket cased New Willard also with an electric motor.

The issue is that if I plug them into the wall one way, the case is energized with 120 V AC.
If I flip the plug, they have a few volts but as the motors power up the volts also go up to about 30 V AC.

We never got shocked testing and running them until I took the Singer down stairs in the basement to work in it and stood on the cement floor!

I have added a grounded plug so it will not power up to 120 V from the start, but wonder what the issue is.

I assume the possibility is remote that two different makes and models machines would show the same issue.

I tore the Singer motor down repeatedly and tested it for continuity from wires to motor case and it shows no continuity, over and over, but the case still powers up!

I was thinking that if back in those days, it was not likely that the user would be grounded working on their wooden floor, so it might not have been considered much of an issue?

I'm sure that there were fewer safety procedures back then compared to today because of the lack of experience and knowledge.

Any ideas?