Start with the basics. With the car idling, what is your voltage measured at the battery? Have your battery charged then load tested. Make sure that plugs are not glowing.

You need to know that alternator and battery are both in good condition before chasing charging problems.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.