Help with a 4.3L TBI V6 (Alternator Exciter???)
 

First of all. Hello!
I have a 1985 Toyota 4x4 with a Chevy 4.3L TBI V6. I have had it for 9 years and it has been a frame off build (see signature for pictures).
A buddy and I were slowly working on it over the years, with him being more of the mechanic than I. He had to move and I am now alone trying to make progress with the truck.
My buddy is the one who wired up everything and I have no idea how to do that, but I am trying to learn.
I don't know what the motor came out of, or what the harness came out of. Is there a way to figure that out?
I am a newb, and I know it. Trying to learn though. (you been warned of newb questions)

The truck runs well however the alternator is not charing the battery. The battery is new (Yellow Top) and so is the alternator.
I am pretty sure it has something to do with the exciter wire.

The harness has a plug that has one brown wire going to it (along with the ground and 12v positive).
https://cimg1.ibsrv.net/gimg/chevrol...4a9da39ab0.jpg

The alternator that I got has 4 terminals that the harness plug plugs into.
https://cimg1.ibsrv.net/gimg/chevrol...40ab98a9f1.jpg

To me it looks like that brown wire from the plug goes to the ECM. I am not positive, been trying to avoid cutting all the harness tubes.

Can anyone help me trouble shoot this?
Probably need help figuring out what specific motor I have and what harness I have.
Then help in figuring out why the exciter isn't working.

Based on diagram, it seems like the brown wire is the Lamp wire.
https://cimg5.ibsrv.net/gimg/chevrol...7c8963f311.jpg
But where does it end up going?

I think I found the wiring diagram, though I don't see Alternator on it.
Am I missing something?

GM Wiring Diagram

Ok here is what I did.
1. Connected the test light's clip to negative and touched the tip to the positive. It lit up.
2. Touched the tip to the red wire terminal on the . It lit up.
3. With truck completely off, touched the prong that the wire connects to. Didn't light up.
4. With truck on accessory (fuel pump on), touched the tip to the prong inside the that the wire connects to. Didn't light up. (none of the prongs lit up the test light).
5. Touched the wire inside the harnesses plug, Didn't light up.
6. Turned the truck on. Multi meter reads 12.02 volts.
7. Touched the wire inside the harness plug, Didn't light up.
8. Touched the tip to the prong inside the alternator that the wire connects to. Didn't light up. (none of the prongs lit up the test light).
9. Connected the test light's clip to positive and touched the prong inside the alternator that the wire connects to giving it 12v. Multi meter ends up reading 16+ volts.

Safe to say that the prong the wire connects to needs 12v but the wire isn't providing it?


Hopefully I did all of this right.