So, I looked at the wiring diagram for the LX150 from the workshop manual and decided I needed to tap into the white and black wire.
Now, I just had to find it in the under-seat area. I did find a couple of white and black wires that were not it - then I looked a little more closely and found a wrapped bundle that appeared to head to the back end of the scoot. I sliced into the bundle and found what I was looking for - the yellow and black and white and black run into the tail light - so I knew I was in the right bundle. I snipped the white and black - installed butt end connectors and then tested the back-off prior to crimping the back off wires (good thing too ) - the included photos tell the story - should be exactly the same for an LX150
I did tape up the bundle again after the install and also zip tied the back off wires after taping to the frame - just to be sure.