Newly installed Light, wiring issues. Won’t turn off
Wire it like this.

Note that not all white wires are neutrals. One of them is part of the switch loop. Once you have identified it, mark both ends of it with black tape or paint.
If you can't tell which white wire is the one going to the switch, it is the white wire that comes into your ceiling light junction box through the same hole, or in the same cable, as the wire you've been calling the &quot;lonesome black wire that’s running to the switch&quot;.
If you still have trouble understanding how this circuit should work, get your library to send you a book on do-it-yourself home wiring, and read the section on switch loops.