Chrysler Repair: 1987 LeBaron Over-Charging: Regulator at fault?, inner fender, logic module

Question
My mom has a 1987 Lebaron, 4-cyl. four-door. The system voltage indicator light in the dashboard was at the top and the red light was on indicating that immediate service was needed.  I took her car to a garage, they ran a test and said the car was over charging, approximately 18.5 volts.  They replaced the computer power module, which they said contained the voltage regulator, but that didn't solve the problem.  They also replaced the logic module with a used one but that didn't help either.  The code readout is 12 and 55 but they said that didn't help them any.  They believe the problem is with the regulator but they can't fix it so they turned the car back over to me.  I'm not a mechanic.  Any thoughts on why the car is over charging?  Is the regulator really part of the computer power module?  

Answer
Hi Roger,
That is a very interesting situation. In the mid-'80s there were models that had a regulator built into the engine power module as well as separate regulators that were mounted on the right side inner fender. It depended upon which model and engine you had. According to the '87 shop manual the only model with the external regulator is Omni/Horizon line of cars. But take a look on the right side (passenger side) inner fender to see if there is a regulator mounted there just in case. I suspect that if it is in the power module and replacing the module didn't fix it, then the wire that goes from the module to the alternator is shorted to ground which in effect causes the alternator to run all the time instead of oscillating on and off which brings down the voltage to the desired level. The shop should have tested to see whether that is the case before replacing the module.* The wire in question is solid dark green in color. So if you go to the power module on the left inner fender and find that wire, then disconnect the plug for it at the module and then you should find that if I am correct the wire is shorted to ground. But it may be that the short is in the alternator, not the wire, so I would  go to the alternator and disconnect the other end of the dark green wire there (There are actually two dark green wires on the alternator, remove both and test both to see if either is grounded).  If not, then see if the terminals to which the wires attach on the alternator are gounded. If they are, then there is an internal short to ground inside the alternator which you may be able to correct yourself, or it will require a new alternator if you can't correct it. Measure for a true short to ground with the lowest full scale reading of your ohmmeter so you can differentiate between a true short to ground and a winding that has a low but still finite resistance. Measure between the end of the wire or alternator terminal and the - post of the battery for an accurate assessment of resistance.
If you find that you have an external regulator by chance, then I would replace that regulator. But according to the manual either the H-body hatchback 4-door or the K-body sedan 4-door are not supposed to have external regulators.
Please let me know what you learn.
Roland
*If you find the wire or the alternator to be shorted to ground then I would say that they owe you restitution for not finding the short to ground before buying and installing the modules. If necessary go to small claims court.