I am not quite sure which post you are referring to.
It would be best if you were to post a photo of this. You don't want to make a mistake.
As a general rule for a Non-Bendix motor:
...... you should see an "S" terminal. The "S" terminal will excite the solenoid field of which will energize the armature and kick the pinion gear into the ring gear.
...... you may also see an "R" or "I" terminal. If so, this will by-pass resisted ignition coil voltage.
.
I picked up a IMI Hi-torque starter not too long ago to replace the old style bendix drive. The new one has an extra post to the solenoid whereas the old one just had the post to to ignition.
Here is a photo of what I'm referring to:
