Oh man, been a while since I posted here.
So keeping it short, here's the car: 1987 Chrysler Shelby Z Daytona, intercooled turbo 2.2. As I understand (from previous owner), the car's been modified with a Mopar Super-60 ECU, "purple" cam, and retrofitted cruise control. (I'm not sure if the power windows or power locks were retrofitted. I believe the A/C is stock.). The ECU is the power-module + separate logic-module type.
...and here's the problem: The alternator is not producing a sufficient charge voltage. After a few minutes of running, the "POWER LOSS" light comes on.
Here's what I have done so far:
I checked the alternator's brushes and field coil (while disconnected from the car's electrical); they are good.
At the workbench, I put a current-limited 12V DC source across the field terminals, and with a DC voltmeter on the ground and [+] output, I gave the alternator a few whirls by hand; each time after spinning it, a small voltage was present, that decreased as the rotor spun down. (This tells me the alternator is good.)
Back at the car, with the battery disconnected, I checked for continuity between the [+] batt cable and the [+] terminal of the field harness; when turning the ignition switch to RUN, the meter read 0.5 ohms. (That tells me the [+] field wiring in the harness is good.)
With the alternator connected and the car running, I bridged the field coil [-] terminal to ground THROUGH A 12V LIGHT BULB (to act as a PTC thermistor -- a crude "regulator" of sorts). Suddenly the system voltage increased! The alternator was producing a charge! But the light was flickering...
...so then I connected a small 12V light bulb between the battery [+] terminal and the field coil [-] terminal, and it too was flickering. (Both this test, and the flickering effect of the previous test, tells me the N-channel transistors in the ECU power module that control the alternator's field current (to regulate the output voltage) are indeed working and pulse-width-modulating the field current. And of course all the wiring between alternator and ECU must now be good.)
So here's the puzzling question: With the alternator functional, and the wiring harnesses still good, and the ECU power module still good, why is the system not increasing the field current pulse width enough for a high enough charge voltage?
When I do the ignition switch on-off-on-off-on thing to flash diagnostic codes on the dashboard, I get a code #12 and #16 -- "memory lost / pwr disconnected" and "loss of battery voltage", respectively, according to the Haynes book. (I believe the #12 is typical after the battery has recently been disconnected from the vehicle. I dont know if #16 means the same thing, or if #16 means the ECU is sensing the voltage never increases to a sufficient level to charge the battery.) Anyhow, there are no other fault codes.
Where could the real fault be?