won't start....

Do you have a newer transmission than (I forget, ) 69? The older autos must have the SINGLE pin neutral switch, the newer ones 3 pin. The center pin has a wire that runs up and grounds the starter relay in park/ neutral

Could be wrong neutral switch, shifter/ linkage not correctly adjusted or something amiss inside the transmission

And could be electrical.

Simple circuit: Twist the key to start, the yellow "start" wire comes alive and feeds power TO the start relay on one of the flag "push on" terminals. Power goes through the magnetic coil, comes OUT the other flag terminal, runs down the wire to the neutral switch which should be ground.

So to troubleshoot, try removing the NSS wire and clipping a jumper to that starter relay terminal and ground. After making certain you are in P/N, see if it cranks.

If not make certain the yellow "start" wire is hot with key in start.

Also clean your batter terminals, check starter relay stud and starter big stud for tight connections, etc.