unclereggie wrote:The other two contacts exiting the switch give the same reading (0.4 when on, zero when off) ...
Taking this at face value, this does not make sense!
What you are saying is that with the switch 'on' you are measuring 0.4Ω, which is reasonable and is comprised of two parts - the resistance of your test leads plus the 'on' resistance of the switch contacts in series.
However, you quote a reading of 0Ω when the switch is 'off' which is not only a dead short but is also less than the resistance of both test leads connected together! Unless you have a zeroing function on your meter to null out the resistance of the leads, I would expect to see some residual resistance reading, even if you are using nice thick test leads!
What I think you meant to say is that in the 'off' position, there is no reading - which means ∞ (infinity) or open circuit and is the exact reverse of 0Ω!
I think in successive posts that some have interpreted you literally and assumed a short circuit whereas others have mentally corrected your error and treating it as open circuit (infinity) which causes even more confusion!
You probably won't be surprised to find out that you are not the first to cause exactly the same confusion!
Remember, when posting, to get these things right - if what you say isn't clear, my computer screen can't answer back any better than anyone else's when I mutter "What the ...?"