won't turn over after battery and starter replaced

Thx for reply DaveJM. I misspoke and should have used the term 'pop the clutch', not jump-start, when describing ability to start car. It simply will nor crank, although there definitely is both 12V and ground at the starter housing. The 'wire' that must trigger the starter to carry the electricity is inserted but has no juice flowing when key is in START position --- is there a relay involved, or does the ignition switch have to pass a signal into/thru a control module to activate the starter? (In trying to decipher components involved, I can't find a decent wiring diagram online that depicts the ignition-to-starter system flow.)