Have you checked for "Dirty Battery Terminals"? That is where to Start. Also, check for voltage at the Starter Solenoid Terminal using a person to turn the Ignition Switch to Start position. Often on a vehicle that is older, the Starter Solenoid can be literally frozen up with corrosion and cannot move when energized. If you are not getting 12 Volts at the Solenoid then you could have an open connection between the Ignition switch and the Solenoid. The firewall Connector and anything from the Ignition Switch to the Solenoid can be corroded or otherwise causing a high resistance or Open Circuit. Neutral or Clutch Safety Switch cold be out of adjustment and/or defective. If you cannot perform these simple tests, see a Professional ASE Certified Technician.