Ignition Issues - Car Won't Start Intermittently

I agree with checking the NSS itself (i.e. right at the switch, not the wire from it). I would add, that you should disconnect the shift linkage when doing this. The transmission itself has spring detents for each position. You want to align these with the spring detents in your shifter. If not, the NSS may be correct that you are not fully in P or N, and is doing its job protecting you. Whenever you bypass the NSS, do not have anyone standing in front of the car when you try to start, because the car may jump forward. If you don't have a multimeter, go to Harbor Freight with a free coupon.