A little help here...

My 74 Duster still has a starting issue...
I will turn the key and the car WILL NOT CRANK.
It will fire right up one day and not the next.
A little help here?

New parts...
Voltage regulator
starter
battery
neutral safety switch
starter relay
key switch
resistor
electronic ignition
Coil
All 74 seatbelt lock have been removed or disconnected.
Ive gone thru all the wiring too.
All grounds are good.
Please help....