hi, FEGEITOK, I searched online and found this thread. My 2000 Mazda MPV worked well. I replaced the two valve cover gaskets. AFTER THAT I got P1520. I think my harness was not melted like yours but was in a bad condition. When I pull out the valve covers I must have bent the harness and caused the wires shorted. I am wondering how you found the short place. Should I cut off the harness plastic tube and tape and then visually examine each wire inside inch by inch? Thank you.