I plugged in all the wiring, but there's one loose wire that I don't know where it goes. It looks like a ground of sorts, but why would a plastic turret need ground?

It's the right-most wire in this picture.
The recoil system also doesn't work. The flashbulb flashes instantly when I push up on the left stick, but there is no recoil function and the barrel doesn't move from the fully retracted position, as it is in this pic:

What am I missing / doing wrong?
It's the IR version of the turret; I don't care about the IR functionality, I just want the barrel recoil to work.