if you finally figure it is your ecm---you have a choice of buying a new unit or making the alternator a 1 wire with a trans-po conversion $35-----guys doing cummins conversions to older vehicles use these all the time---my son orders them 3 at a time when the price is right just to be sure to have them on hand when needed-----one time he ask to grab the one off my 69 gmc/cummins to get a customer on the road the same day-----if you want to see what it is--- just keyword cummins alternator regulator on ebay---they show up on amazon as well---it is the little silver box with 4 wires that fits inside the alternator case.....