Cadillac Repair: not charging, electrical schematics, simple test

Question
I have an 83 Seville, and while driving along at night everything just got dimmer and dimmer (faint no charge light came on) until it chugged along and died.  My mechanic has put in five different alternators and can only get it to charge to 12.35 instead of over 14.  Any clues as to what it might be?  All the other electrical systems seem to be working.  If you need other information, let me know.  Thank you very much

Answer
All you need is some electrical schematics, Some simple test procedures to do and some telephone assistance if necessary.

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