Dinked around with it today for several hours,,, Cleaned all of the cable ends there are,, changed the battery since it was pretty old & weak,,, was checking the 2 small wires that go to the alt,,, and tested them from the alt end to the pcm,,, ohmed great,,, but was not getting a voltage signal from the grey wire at start up,, which is suppose to happen for the first 10-15 seconds,, just long enough to excite the alt and make it start charging.
Still missing on #3 & #4,, and since all indications was leading back to it being a bad ICM,, I ordered one from Advanced Auto,, the new one I tried the other day was for O'Riley Auto,,and it didn't fix the problem,, so I held my breath & FINALLY,, she started running properly. The scanner said that #3 was still misfiring a bit,,, so I swapped the wire with a different one we had lying around & the miss went away. Noticed a few other cylinders had occasional misses also going on, so we got a new set of wires and all is now good,, no more misses,, AND as soon as I had changed the ICM,,, it must have told the PCM that all was good in the world, because the alt was alt'n 14.5 volts steadily,, even on the inside gauge.
I had called our local electrical shop,, and was told that would most likely happen,,, the alt will sometimes not fire up if the pcm notices a problem with missfiring,, and he was right.
Finally,, at least for a while I can relax on this car,,, at least until the next issue arrives. Thanks for all of you who gave me suggestions!
65 Mustang Restoration
My other project.