Here is what my junction looks like. I do not have the metal crimp but the junction is soldered. I also do not have the black wire with white stripe for the ammeter because I have a warning light dash not a gauge dash.
Here is a diagram like yours that shows the ammeter shunt on the left side of the diagram. It tells the ammeter whether the voltage is greater on the battery or the alternator. In other words whether the alternator is charging or the battery is providing the power to the circuits.
In order to do this the ammeter wires have to be connected to the main junction and to the battery positive side. See the diagram. If you connect the alternator to the starter post then the ammeter will not get a correct reading of the voltage difference between the alternator and the battery.
The shunt wire also serves as the charging wire for the battery which would be accomplished as well by connecting the alternator to the solenoid with the large cable from the battery positive.
A common misconception is that the battery supplies the power for the truck and the alternator just charges the battery. They always want to run the alternator charge wire back to the battery positive post or to the starter.
It should run to the main junction to feed all the circuits with a small wire connected to charge the battery.
When GM went to the next generation trucks with the voltmeters they ran the alternator charge wire to the solenoid with the big battery cable and then ran two feed wires off that, with fusible links to feed the rest of the circuits.
Here's a diagram I like to post that shows a real good way to wire our trucks when we go to the high draw loads like cooling fans. I modified it to show how to wire it and keep the ammeter.