Mystery blue wire bypassing the NSS

Eons have passed and its time to make it safe to start. The car is scheduled into a movie shoot and stranger(s) will be driving my AMC. weird right. 72 Jav sst 360 auto, owned since 92 wiring is all factory. Seems all this time a phantom dark blue wire w/(white)tracer attached (factory crimped) along with the black wire (runs to ground terminal on the start sole.) at the engine harness side of the neutral safety/backup switch harness has a continuous path to ground, 56ohms to be precise. The switch works fine but its basically shunted to ground by this undocumented wire. It's nowhere to be found in the 72 FSM (schematic). I'm certain the NSS will operate proper if I cut this wire out. But what is its purpose? Where does it land? Appears to be running toward the firewall junction block. 

A nice citation for who helps solve and get the SST on the big screen!  

 

 

The diagram shows a wire labeled "Automatic Transmission Only".  I would say that is your blue wire.

Its obvious that the Tan wire provides the power from the fuse panel.

Black is usually ground, but where does that black wire go in the diagram?

The Brown wire is probably the one next to the Tan wire in the connector, but again, where does it go in the diagram?  And what might the "DT" label on the brown wire mean?

This is from Eddie Stakes site and it makes more sense with the color codes you have.