Chrysler Repair: Charging problem with 97 2.5L, digital voltmeter, oxygen sensors

Question
Started the car last week and drove about a mile.  The battery light came on and the engine died within a minute or two.  I supspected the battery had an internal short, but when the battery was disconnected and the car was jump started, it died as soon as the jumper cable was disconnected.  I figured the alternator was not working.  I replaced the battery and checked the voltage at the battery terminal.  It was about 12.8 volts with the engine off and 12.4 volts with the engine running.  I replaced the alternator, but the old one passed the test at the parts store and the new one still gives a battery light.  I checked the voltage at the battery terminal with a digital voltmeter and the reading was jumping around between 12 and 15 volts.  I suspect the voltage regulator is not working, but since it is part of the computer, I would like to be sure.  Can you tell me how to troubleshoot the problem, like check contnuity from A to B, measure voltage at point C, disconnect something and make a measurement, that sort of thing.  It is my understanding that if the voltage regulator is defective the computer has to be replaced and programmed by a chrysler tech.  Any help would be appreciated.

Thanks, RJ

Answer
Hi RJ,
The alternator control circuit is via the field coil. One end of the coil is attached to the autoshutdown relay (which also provides current to the spark coil, fuel pump, oxygen sensors, fuel injectors, provided that the engine is running successfully) and the other end is either grounded (to create the magnetic field) or at 12V (to shut down the field), which essentially is a rapidly oscillating control that results in the desired regulating voltage as determined by the computer. The dark green/orange wire at the alternator connects to the pin of the ASD socket that is closest to the middle of the power distribution center. So you could check that connection. The dark green wire at the alternator connects to pin 8 of one of the plugs at the computer (plug pins numbered 1-40). If those are OK, and the ASD is not flaky (you would hear it clicking if it weren't), then the last thing to check would be the red wire from the alternator to the battery + terminal for any sign of intermittency. There is a fusible link (a wire that acts like a fuse) in that pathway so shake the harness a bit.
You could also get a fault code readout at an Autozone parts store (usually free) or at an independent shop (~$40) and see if the computer sees a problem with the charging circuit. Let me know the fault code and we can go from there if that is so.
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Roland