You have to test x27 center pin [ vi/w] with test lamp while connector is plugged in so that the circuit has a LOAD on it.
If the test lamp goes out with the load on it , the suspect is bad contacts in NSS or Ignition sw.
You can have a 12v test lamp verify 12v at pin from NSS or Ign. sw. , but it will drop out as soon as the starter sol load is applied.
You know the circuit is good from x27 downstream b/c you can jumper starter circuit from x27 with 12 v bat supply..............................
A trick I use is to hold the Ign sw in the start position with left hand while moving the shift lever back and forth at N or P ...if starter kicks in, NSS is suspect.