I believe the lower harness contains only 6 leads: a thick cable for the alternator and one for the starter; a thin wire for the alternator and one for the starter; an oil pressure sensor wire and an oil quantity wire. Maybe this will help you troubleshoot.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles