Check your engine grounds and engine harness ground. Also, could be a bad ignition switch or clutch switch.
The clutch switch is above the clutch pedal. The easy way to test the clutch switch is to unplug it and jump the wires together. Make sure the car is out of gear and turn the key, if it starts or tries to start with the clutch pedal out you switch is bad or misajusted. If your car has cruise control there are two switches I believe the start clutch switch is white and the cuise clutch switch is yellow?
The ingition switch is attached to the back of the ignition key lock assembly. Remove the lower and upper steering column covers. Then using a small phillips screw driver unscrew the two screws that hold the switch on. Use a flat head screw driver in the pac-man shaped hole and turn to start the car. If the switch seems sloppy or turns from the start position to and goes back to the accessory position the switch is bad.