Depending on the serial number Clark used
Several nsc controllers (neutral safety control )
The symptoms are , no forward , no reverse , no forward or reverse again depending on serial number look below dash to left side
That is where it is located and other response was correct down close to hyd valve are two diodes one for forward one for reverse and if it has 2 amp diode replace with 5
Also some went thru dash pod before they went to trans solenoids the first place I would check would be the plug on the column if you had a schematic for wiring you can trace the wire from switch to solenoids and running wire to solenoids from switch is not a good idea you are bypassing the safety protocol in place