Alternator

The two field terminals work the same way the older electronic regulators did. Wire it the exact same way your truck's two field wires were connected. This would be the same for older cars too, with solid state electronic regulators.
This Magnum alternator does not have an internal regulator. That is why it works this way.
The diagram above is correct. The one that says ground - terminal was a ground cable, but I forget where the other end went. The one that says wire harness hold down is just clamp to support those wires, nothing more.