Some background, I was replacing my starter morter on my 98 Z34 and noticed that there was a cable/sensor that was just hanging around and I can't seem to find its home.

it looks like it splits off from the starter motor harness if that helps any

Here are some attached pics.

 

Well I been looking in my service manuals and I have not found it yet.
It doesn't look like a sensor to me, kinda looks like a cable that maybe would spin. But I am not sure? I will keep looking!

 

Id bet thats the knock sensor plug.

Take a look at the front knock sensor (screwed into the side of the block facing down) and see if theres a wire running to it. I can't think of any other 1 wire plugs anywhere near that area besides the knock sensor.