Measure the resistance of the wires to see if that one is comparable.
Carbon tracking is often a very thin line on the coil tower phenelic. You can feel it with your fingernail. The coil tower may also be cracked. If arcing continues, a narrow black line is cut into the rubber of the boot.
The point is, high voltage jumps at the closest point and the plug is usually that place. Either the spark is having trouble reaching the plug, or there is something conductive at the coil tower/boot area - ie. - carbon tracking.
