Neutral Safety Switch
Juice, I agree with small P - it was a bit of a pain, but it'll come off. put the nut on a few turns and then try again.
One note, I was able to clean mine without removing it from the truck. I unplugged it in the engine bay, but didn't snake the cable all the way back (too lazy). Just be careful you don't lose the little brass contacts on the arm. Also, be sure you align it right when you re-install it. With the trans in Neutral, the scored line on the NSS case should be in line with the shaft the NSS mount on. If you don't align it right, the back up light still won't work (been there, done that).
btw - don't take this this wrong way, but you did take the top bolt out, right?
Good luck,
Andy