I have been rebuilding a 1993 mustang for about a year now. One of the most significant things about this car's rebuild is that the guy who owned it before me put a wiring harness out of a 1990 or 1991 into the interior without changing the rest of the wiring. I got a 1993 4-cylinder wiring harness, which seemed to fix the myriad of problems I was having....after I fixed the fusible link that was popped when I got the new harness; did I mention I have really bad luck with this car. I have it running fairly well, but when I took it in for a smog the tech noted that the check engine light would not turn on when the key was in the on position; without the engine running of course. After checking further, I discovered that it will not display the 11 or 111 code to my OBD I code reader; like the computer was not communicating with my reader. I did note that when I turned over the motor to start it, the check engine light comes on then immediately goes off when it starts or I let go of the key. Per a thread in this forum, I checked the ohms from the grey with red stripe wire of the diagnostic port to the negative battery cable and got a reading of 1.8. When I checked the ohms between pin 46 of the computer to the same wire on the diagnostic port I got 13.5 ohms, which fluctuated a lot without doing anything to it. The thread says I have a wiring issue but I don't know what to do from here...What should I do?