What make you think its the NSS-the switch only function in P/N that's its primary purpose preventing the engine from cranking over in other gears. When you say won't trun over-are you saying its cranking over and will not start or just won't crank over at all/nothing when you are in cranking position? Let me know or go to this link for further information- https://www.2carpros.com/articles/car-cranks-but-wont-start

The NSS is located on side of transaxle case.