The point of making the measurements was to learn how to use a multimeter to discern between the L (lamp or the switched source) & S (sense or battery voltage) terminals on an internally regulated alternator.
With the positive probe on the meter on the S terminal and common on the B terminal, you will see resistance. In this case I'm using a ZX alternator for the demonstration.
However, if you swap the probes, the diodes in voltage regulator will block the resistance reading between the S terminal and B terminal. This meter reads "OL" or open line when the circuit is open.
There are no diodes between the B terminal and the L terminal. So the reading get with the positive probe on the L terminal will be about the same as when the common probe is on the L terminal.
In your second photo, the common (black) probe is on the S terminal.
Frankly, I would connect the wire from the S terminal to the cross of the T terminal on the stock wiring. Connect the vertical on the T connector to the L terminal. Again, you can get the connector from Vintage Connections. Get the jumper plug from Motorsport Auto. Hook them up. You are done.