I have a 82' 280zx that I have replaced the starter and ignition switch. I turn the key which will bring to life the fuel pump, fuel injection and spark, but in order to start the vehicle I have to arc the starter with a screwdriver. I have tested the relay and swapped it with another used one that I have to no avail. Should i check the engine harness next? Or is there potentially something else I may be missing?

Any help would be appreciated. 

Thank you!!

See if the little yellow wire to the starter solenoid has voltage when you turn the key to Start.

Some of the cars have an inhibitor switch.  GL model with automatic transmission.  Otherwise it's just a yellow wire from the ignition switch all the way to the starter solenoid, with one connection along the way.  The connector would look exactly like the picture, with 21 pins.