I got this from the service manual. Please take the time to read it.
Power is supplied at all times
to ignition switch terminal 1
through 40A fusible link (letter e, located in the fuse and fusible link box).
With the ignition switch in the ON or START position, power is supplied
through 10A fuse [No. 18, located in the fuse block (J/B)]
to park/neutral position relay terminal 1.
Also, with the ignition switch in the START position, power is supplied
from ignition switch terminal 5
to park/neutral position relay terminal 3.
With the selector lever in the P or N position, ground is supplied
to park/neutral position relay terminal 2 through the park/neutral position switch
from body grounds B55 and B75.
Then park/neutral position relay is energized and power is supplied
from park/neutral position relay terminal 5
to terminal 2 of the starter motor windings.
The starter motor plunger closes and provides a closed circuit between the battery and starter motor. The
starter motor is grounded to the engine block. With power and ground supplied, cranking occurs and the engine
starts.