my 1984 190e has had some engine wiring harness issues. I found the wires from the coolant sensor were decayed inside the harness about 4 inches back from the sensor plug, did not find it until the wire broke. you can check the condition of the wires by removing air cleaner assy. and [B]carefully[B] cutting the outer covering back to inspect the wiring. After inspection just use electrical tape and wrap the cover back on the harness.
hope this helps.
Joe