Electrical Questions? Ask an Electrician Online.
Welcome. My name is ***** ***** would be glad to assist.
In order for the motion sensor to operate, power must be applied through the switch to the fixture.
Since this is being added to existing lights, there is no way to power it unless the other lights are on.
If you can get a separate power to the new motion light, then it could operate independently.
But it will take full time power for the motion sensor to operate.
Hope that explains, let me know any questions.