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The original post and #6 do not provide a clear definition of the desired logic.
From post #1
6 can lights total. Light 1, light2, light 4, controlled from first switch. Light 1, light2, light3 controlled by second switch . Only Light 4 controlled by 3rd switch.
What is the definition of "switch"? I am reading this as singular. Then I make the assumption that this single switch is a SPDT center off with spring return to center.
Still from post #1.
All lights 1, 2, .... 4 are simultaneously turned on or off from switch A no matter what their previous state was.
All lights 1, 2, 3 .... are simultaneously turned on or off from switch B no matter what their previous state was.
Light ................ 4 is ....................... turned on or off from switch C no matter what its previous state was.
There are no lights 5 or 6.
This is an application for GE RR relays with appropriate logic. With reasonable probability they will have 50 year life even with most lightning storms.
From post #6 things have changed some.
All lights 1, 2, ... 4 ........ are simultaneously turned on or off from switch A no matter what their previous state was.
All lights 1, 2, ........ 5, 6 are simultaneously turned on or off from switch B no matter what their previous state was.
Light .................... 5 ... is turned on or off from switch C no matter what its previous state was.
Light ............ 3 ........... is not switched.
The only way to switch light 4 is from switch A, and light 6 from switch B, and light 3 can not be switched.
We need an accurate definition of the required logic.
Note: it is not necessary that the on and off function from a specific switch be the same for both on and off.
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