I have a 95 E320, and I just changed out my wiring harness. Got it from Phil at Fast Lane.
Yes the wiring harness includes the wires with cracked insulation leading to the spark plugs.
It's not that bad a job, about 2 hours. Any DIYer can do it. Lay out the new harness over the old to help with the routing.
Good luck. Be sure to give Phil the VIN number, as the early '95s had one harness part number and the later one another. Better yet give Phil the P/N for the harness, located on the harness just behind the battery. That way you will be sure to get the correct P/N.
Since all of your troubles started with the plug change, and you have to move the harness around a bit to change the plugs, I would start there.
BTY, my e320 has 126 kmiles, and at about 121 k miles, I had to change out the O2 sensor. I also had to clean out the EGR line between the EGR valve and the intake manifold. It plugs with carbon deposits just where it enters the intake manifold. Access to this connection is from below, and the tube is held in the intake manifold with 2 10mm hex bolts.
Good Luck - its a fine riding car - but it needs a bit more TLC than a rice burner!
1995 E320 Sold at 288kmiles