I am using Pi3+ with openhabian + USB Z Wave stick. AND a home security LED flood lights AEC-34QA2-AC16W.
What I need to do is wire into my dusk to dawn Led flood lights, motion sensor, to know via z wave when the motion sensor is activated. Sense the 120V output of the sensor.
Any suggestions?
I have yet to see a sensor that ouputs 120V…
So you have a motion sensor, is this motion sensor the trigger for the flood light and I assume this has no zwave capability? I would just tap into the PIR sensor itself and use an ESP8266 since PIR sensors are mostly just transistors that opens the gate and allows current.
If you want to detect the 120V passing through all the way to the lamp, you need a transformer for that to bring it down to a level readable by a voltage detector.
Or check what relay the PIR sensor is activating and check when the coil is energized.
You can get a Zwave micro relay and wire it up to sense the 120V if you are comfortable with the wiring. An example with a motion sensor is here. Sample relay is here. I’ve never done this, just reporting what others have done.
Or just put in a photodiode connected to an ESP8266 and only trigger the Rule when it sees bright light after the sun goes down. As an added bonus you get a measure for cloudiness during the day. 
It wont give you exact lux or anything like that but for this I don’t think it matters.
Thanks guys for your help. Maybe I didn’t explain enough trying to keep it short. My bad! John you are on track I will explore your suggestions. I want to sense the 120V coming from the motion sensor to the lights. When motion is detected. I want to do this day or night by turning off the LUX control so the detection works 24 hours a day. And this gives me more diversity than just lighting. Thanks again guys.
Are you looking to DiY it or just purchase one? You have many options to detect voltage, an optoisolator, clamp on voltage sensor, etc.
Given the way mass production affects prices, it may be better to abandon trying to tap into the dedicated lighting PIR and install additional PIR with the technology of your choice for your secondary purpose.
Lucky, cheap is the name of the game to accomplish my goal. 
DYI is good. John’s suggestion seems good at this point in time I will do more reading. The relay he recommended is great (if as I have read so far) the relay reports change to my OpenHab via Z wave. My thoughts at the moment is OpenHab will do all the work, BUT I do in vision NOW more possibilities with the dual relay version, but I want to stay on track. By all means if you have a lesser expensive or better option, I am ALL ears. More knowledge is better. Even for this ole 70 year old tech.
Well a cheap, but reliable route, if this was my project, is a $3 wifi-capable ESP8266-01 but you will need to dissect your sensor. Your sensor will have a relay that gets activated when there is motion. That’s basically how the light turns on.
The sensor should have at the very least 2 wires, a ground, and the signal. You just need to tap into those and wire them up to the ESP8266’s gpio/input pin. Then you just code the ESP8266 to update OH either via REST or MQTT
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Thank You John Schmitz, your suggestion and links which led me to a simple, quick and relatively inexpensive solution. Not only for the question asked but for more projects on my list. I ordered two types of multi switches, a QUBINO Z-WAVE PLUS FLUSH 2 RELAY MODULE ZMNHBD3 from “The Smartest House” which arrived and worked great and a VISION Z-WAVE IN-WALL 2-RELAY DOUBLE SWITCH ZL 7432US from Amazon which hasn’t arrived yet. So thank you Again These are awesome devices!