Is it possible to link motion-activated flood light fixtures?
I use separate detectors from lamps, and here's how I wire them.  

First, I use the type of sensor which has its own neutral (rather than the type which has no neutral and sits in a "switch loop".)  This is very important. The sensor needs to be able to power itself independently (via hot and neutral) and not care what if anything is on the output.  

I run 4 wires down the length of all the sensor and lamp sites.  The 4 wires are: 


Green - Equipment Ground
White - Neutral
Black - "always hot" 
Orange or Red - "switched hot" 




I connect ground, neutral and always-hot back to power supply at the service panel. 

I attach each sensor to always-hot, neutral and switched-hot. 

Each lamp gets switched-hot and neutral.  If the far end of the string is all lamps, you don't need an always-hot. 

Grounds everywhere grounds go. 



When you are working with integrated sensor-lamp combos, it depends a great deal on how they are wired internally.  Some are assembled from common off-the-shelf 120V components, and will keep the functions reasonably separate and you can access them.  Others may vary. For instance, LED sensor lights almost always use LED emitter heads that run on around 12V, often constant current; so they use a 12V-ish power supply.  They run the sensor off that 12VDC, for the simple reason that 12V sensors are cheaper than 120V ones.  

If the sensor part doesn't work for you, but the other guts do, you may be able to bypass or replace the sensor - a great many screw into fittings like this, and  you may be able to retrofit your light with a different sensor.