Both engine wiring harnesses and all plug wires were replaced about two years ago with factory parts when the engine was runing very hot and going into limp mode. The local Mercedes shops were no help. It turned out the catalytic converters were both bad causing high back pressuer and extreme engine heat. Both wiring harnesses had started to crumble and I did the coils, caps, rotors and plug wires as I suspected the heat had gotten to them. Very expensive problem, but I can say the wires should not be an issue.