I’m not exactly sure how the brown exciter wire works on a truck with a volt gauge and no idiot light. The way an alternator exciter circuit works with a light is ignition power goes to the idiot light, out the light on the brown wire to the alternator. That’s what the regulator sees to know the ignition is on. Once the alternator is spinning, the regulator is suppose to apply power to the brown wire. Since you have power on both sides of the light, it stays off.
The regulator supplies a ground when the alternator is t charging. That’s why the light comes on with the ignition on, engine off.
I have never check voltage on the brown wire with the engine running, so I have no clue what it will show.
Did you verify voltage at the alternator stud? With the engine running, it should be around 14 volts.
