The 1586000-4: The locking ramp fastening gives an audible click when fully mated, so a half-seated connection is obvious before the harness leaves the bench.
Contacts — the part that trips up a BOM line
This housing ships without contacts — the listing note is Contacts Not Included. You order the crimp terminals separately.
Mating half and keying — what locks and what doesn't
The plug mates with the VAL-U-LOK receptacle housing that accepts the matching female crimp terminals. The locking ramp on the plug engages a corresponding latch on the receptacle.