mbsteve,
hard to believe that the new harness would also be defective, but one never knows. I would check the wires that branch off the harness to the fuel injectors, I guess they would be under the shroud and sitting in the area of the intake plenum, where its real hot.

You would have to split open the outer sheathing to have a look at the actual wire insulation. If its bad there its bad elsewhere.

Can't hurt to have a look.

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1995 MB E320 Wagon
2001 BMW 530i
2007 MINI Cooper S (!)