2 wire switch

[buggy]

It may have been switching the neutral, you would not read voltage and still able to switch off/on. No voltage reading maybe because no hot(ex:positive) available. Still would have two wires, one incoming neutral(ex:negative) and one dead wire outgoing from sw to whatever device was connected. When switched on it carried whatever load was conected. That is not correct according to present day codes, but that was done on the old 2-wire knob and tube wiring jobs all the time. Switching the hot or neutral was allowed back in early 20th centry.