I have been away for a while (poorly) and have only just caught up with some of the posts on the Vintage thread. A good number of posts are about 221k and or electrics on other vintage machines. Firstly there is one rule of thumb. Never trust electricity, it will always find it's closest way to ground and this may well be by it travelling through you! The wiring you are trusting on a 221k etc may be 50, 60 or 70 years old. The mains cable and foot control cable was rubberised and will most likely be rotted by now. The insulation on the machine side will be brittle and if you combine the two together you may well end up with a machine that is just live and when you touch it.. well you will know about it!
I have rewired, capacitor removed and restored more vintage machines than I can remember, into the hundreds now and now I am on the mend I shall be back doing more. I am not plugging myself, not at all. I just wish to make you aware of the potential risks. Where electricity, metal and people meet there will be only one that gets hurt.
Barny