Chrysler Repair: Voltage Regulation on 89 NY landau 3.0, engine controller, speed motor

Question
Hi, I changed alternator and battery already, could be my voltage regulator? and where is it located. pRoblem is that, when A/C compressor kicks in, the voltage would eventually keeps dropping from 13.7 when I'm on red light or when stopping many times. Seems like the battery is not getting enough charge during these times on idle mode, sometimes the engine would stall and I have to turn A/C OFF and re-start engine fine. If on highway, no problem because of course the alternator is spinning faster. Any thoughts? THe belt seems to be tight which I thought might be slipping. HOw about my idle RPM? Isn't it that when there's more load to the alternator, the computer would make the engine RPM should go higher to compensate? Thanks in advance. I hope i gave enough info for you give me good response

Answer
Hi Fred,
The voltage regulator and the idle control on that car has already been centralized in the powertrain controller so there are no separate parts to consider. Nontheless it could be an issue with the wiring to the alternator or to the automatic idle speed motor. The controller has a memory in which it stores coded fault messages that describe malfunctions it has detected.  The most useful thing to do would be to try to get the fault codes that may stored in the engine controller memory to readout. Try using the ignition key: turn it "on-off-on-off-on" and leave it "on" (doing this quickly, no longer than 5 seconds). By "on" I mean just the normal position when the engine is running, not the cranking position. The 'check engine'light will remain on when you leave the key in the "on" position with the engine still not running. But then watch the 'check engine' light to begin flashing, then pause, flashing, pause, etc. Count the number of flashes before each pause and keep track of the numbers. Repeat the readout and verify the counts are correct. Then group them in pairs in the order that they came out, thus forming two digit numbers. You may notice that the pause is shorter between the digits of a given number, and longer between the numbers themselves. Then send me a 'follow-up' question telling me the results of your readout. By the way, 55 will be the last number (two groups of 5 flashes each) and that is the code for "end of readout".
I have the troubleshooting manual for the 3.0L engine and we can look up the possibilities of what is wrong based upon what fault codes you show. There is also an essay on fault codes at the site:
http://www.allpar.com/fix/codes.html
which gives the meaning of the code numbers. But then you need to get specific info for what exactly might be the diagnostic tests or parts to replace to complete the repair.
Roland