I did get lucky when I bought the van it came with a Chrysler factory manual

So I put the new reman alternator in. I ran two more grounds from the fire wall to the engine and to the alternator it self. I found a meted wire that went to the egr control module/ oil pressure switch and a sensor in the intake. And the wire runs into the main harness. Being as though the egr has been removed I removed all the wiring for it and fixed the portion of the melted wire than was attached to the oil pressure switch. And now it stays steadily at 14.5 v +- . Seems to be charging better than ever. Thanks to everyone telling me to check for grounds and voltage drops.

My 79 W150 has a full flo type ammeter

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81 LeBaron Salon,88 5th ave,79 Aspen SE wagon,79 W150
Don't worry, nothing is going to be alright.

Have you verified that by either disconnecting it and seeing if the truck still starts or with a wiring diagram?

Digging up a old thread. This seems to be my issue as well. I’m bumping this so I can use it for reference. Thanks for these and the search function worked this time!!