Just curious–what part determines which position the shifter is in? Is it the neutral safety switch?
Nope. It’s the arrangement of the levers on, and in, the transmission. Problem?
Could you tell us a little more about why the question.
You determine what position the shifter is in by moving the lever.
The lever you move just communicates what you do to the "shifter" (BTW what exactly what part are you referring to as the "shifter?"
The neutral safety switch detects where it is.The driver determines what position the shifter is in.
The Transmisison Control Module (TCM) determines what gear the transmission is in.
In a manual, the shifter determines what gear the transmission is in.
The neutral safety switch just prevents the engine from being started with the drivetrain engaged. If it’s messed up it can create starting difficulties.