See if you can peel back the protective sheath on some of the wiring to take a look at the insulation. It should then be obvious. If the insulation is cracked and flaking and you see bare copper wire, then I recommend changing the wiring harness with a replacement. You can get one for $650 from PartsShop at the top of this page. Mine was more expensive since it's a later production model.

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95 E320 Cabriolet, 159K