I am putting five LED can lights in my ceiling and would like to know the best way to power them. I have access to a junction box with two fixtures in it, one is a three way, the other is a single light. I also have access to a can light that I don't want on this series of lights. can I access the power in the can light and run a switch off of it, or will that control all of the lights? I can fish a new switch down the wall and put it next to the old can light switch. I'm not sure about tapping into the junction box, because when I turn off the breakers, my Klein voltage tester still shows power in it, flashes red and green.

 

If that is a junction box with two switches then there could be two distinct circuits there on two different circuit breakers.