Chrysler Repair: Alternator trouble: voltage spiking high, voyager 3, field coil

Question
QUESTION: We had the a transmission jerking issue and was told it was a alternator power problem. This would happen only when the check engine light would come on, as long as the light was off, it shifted smoothly.  We changed the alternator and the trans runs smoothly, but now the voltage needle keeps spiking over 18v, and 2 codes have come up , #41 and #46, I've read what they are, but not sure where we should go from here, if it were the pcm or ecm why would the voltage have been spiking before.

ANSWER: Hi Randy,
The spiking high is a sign that either the field coil in the alternator is shorting to ground, or the dark green wire between the field coil and the ecm/pcm is shorting to ground due to a break in the insulation. I say a dark green wire but I don't know for sure because you didn't state the year or the engine but that is the typical wire color used to oscillate the field coil which is how the voltage level is controller. If it becomes ground, either due to a shorted wire or a frank short of the field coil itself, then you will get this overvoltage/spiking behavior. If you didn't have that before then the chances are more that the alternator is defective and should be tested/replaced. But check the condition of the wire at the alternator and as far as you can follow it, too.
Roland

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QUESTION: I did take the alternator back to murray's and their machine said it checked out fine.  It's a 94 grand voyager 3.3 eng.
Thanks

Answer
Well the dark green wire is correct. You could disconnect that wire and also remove the plug at the ecm where you will find the other end of the wire at pin 20. Then using an ohmmeter between either end of the wire and ground see if by shaking the harness you can get it to ground out (read 0 ohms). If not, then the wire is OK and either the ecm has gone bad, or the field coils of the alternator are shorting to ground (regardless of what Murray's says). Maybe the thing to do is explain the problem to Murray's and tell them you are going to buy another alternator from a competitor and if that solves the problem you would expect them to refund your money. Maybe they will then give you a replacement to try. Otherwise, you would be faced with replacing the ecm on a hunch.
Roland