There is a black wire that I saw running along the back side of the oil pan and it was not part of the lower wiring harness (I just changed my harness). The wire was in good shape so I left it alone. I am curious to find out what it is, though. Maybe for the O2 sensor?

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