Don't forget that there is a chance that the excessive resistance is/was in the crimp for the battery cable lug. If you don't have the equipment to make sure the cable is good you might want to replace it, or have a new section crimped on. I think you can get the connection box from a wrecker pretty cheap so I would just replace that.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)