Has anyone checked the condition of the battery? Load test the battery, replace if not up to snuff.

I'm not sure which alternator your car has, but if the connector has blade-type push-on connector, the female side can get weak and not grip tightly enough to keep good contact. I had this problem on my '87 124. My '95 124 is different and has stud/nut connectors on the alternator.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC