Chrysler Repair: 87 Lebaron: weird alternator and gauges issue, battery gauge, field coil

Question
Hello I am having a bit of an issue with my wife's car. She had a dead battery a few weeks ago so I replaced that no problem but then the new one went dead so we determined it was the alternator not charging the battery so I replaced that. when I fired up the car the battery was charged once by the alternator then not again and it would do this each time you started it. So looking through my repair manual I took a shot at replacing the Power Control Module. Now with that replaced when you start the car the battery gauge flies up to the top for like a minute or 2 then drops down to the middle range and the power loss light comes on. It is the same everytime you start the car. It will run but something is not right. Also 2 new problems have come about. The digital gauges cut out sometimes for no reason then come back a few seconds later and the breaks seem softer then they were.
Her car is an 87 Lebaron sedan with the 2.5L

Thank you
Robbie

Answer
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Hi Robbie,
I believe that there is a problem either in the field coil of the alternator or the wires that connect one end of the field coil to the pcm, or in the pcm itself. The voltage output of the alternator is controlled by putting 12v on one end of the coil via the ignition switch when in the 'run' position, and then oscillating the other end of the field coil to ground at such a rate as to produce an average output of 13.6V. If that end is actually shorted to ground then it will put out perhaps 16-18V which is what is happening when you first start the car. I would suggest that you disconnect the wires of the alternator with the battery disconnected first. Then check the two dark green wires for voltage, after reconnecting the battery. One of the wires will show 12V from the ignition switch, the other should show no voltage. Check that latter wire to see if it is shorted to ground or open to ground, it should be open. That would identify the purposes of those two wires. Then measure the resistance to ground of the terminal on the alternator from which you disconnected the no voltage wire. If it shows 0 ohms to ground that is a faulty field coil, shorted to ground, suggesting the alternator is bad. If it shows high resistance to ground then the alternator coil is alright. Finally, rehook the wires to the alternator (again after disconnecting the battery for safety) and then hook up the battery. Then start the engine and observe the voltage on the latter dark green wire. It should be neither 0 nor 12V but rather something in between because of the oscillatory grounding that the pcm should be applying to it. If it is fixed at 0V, and the other dark green wire is higher than 13.6 then the pcm is falsely grounding the wire instead of oscillating it.
The power loss light being on also means that a fault code has been stored in the pcm memory. Turn the igntion switch 'on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the power loss light which remain 'on' to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to assure an accurate set of flash counts, then write back and tell the counts in order of appearance. It no doubt is a code related to the charging circuit.
The gauges/brakes may settle down once you fix the charging circuit.
Roland
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PPS '87 has a mid-year modification which switched from 2 unit pcm (one in the engine comparment, one in the cabin) to a single unit in compartment only. What are the number of pins on the two plugs of your pcm? That would clarify which set up you have.