2002 Chevrolet Astro, V6 4.3, Stock.

Original Alternator at time of purchase was only charging 10v.
New alternator #1 charged at 14v, survived 200 miles. Suddenly, dash showed no voltage, and no battery/charge warning light. No obd2 generic codes.
New alternator #2, still no charge. Was installed with a new and fully charged battery. Bought new scan tool, and was able to get OEM P1638 F terminal code. My scan tool has live data, but I don't see the PID for F coil command/demand.

Checks:
Alternator + to battery - 12.2v.
Battery + to battery - 12.25.
Voltage drop, Alternator + to Battery + 0.025
Voltage drop, Alternator case to battery - 0.00
F terminal to battery (brown?) (Key on Engine off) 1.7v
F terminal to battery (Key on Engine running) 1.7v
L terminal to battery (tan?) (KOEO) - 0.00v
L terminal to battery (KOER) - 0.00v - and no batter warning light on dash (light does work on key on initially)
removed PCM connectors, all clean, no corrosion.

I find it improbable that I've received 2 faulty alternators (no, there was no bench test for the first failed unit) With only 1.7v on the Field Wire (brown?)..... am I looking at a failed PCM?

any additional tests I can complete? I'm about to rename the F terminal from field to... well......

That 1.7V is the reason for the code. It should definitely be higher.

No kidding. It'* worse than that. I went through a wiring diagram, and in my above post, I mixed the F and L wires. All in all, I've got nothing on the F wire. No voltage. Nada. I also have no cluster back lighting, and a no-com with the SRS module. I hope it'* a shared ground, but I haven't had the time to go through a diagram. I dropped it off with a mechanic this evening.... hope I don't ripped off.

2002ish GM trucks/s10/astro'* had issues with ignition switches causing fault codes, trans issues, no start, lighting issues etc.