the prime is a subroutine, it will not always come on everytime you cycle the run position
if it stops cranking, address that first
either the engine seized
batt is dead, or there is a voltage drop on the power and or ground
meter testing will reveal that, once you conclude that the starter solenoid is receiving the signal from the ignition switch
that signal will go through a neutral switch in auto or a clutch safety on a manual
89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.