This is a in depth page, for the Engine Computer fun.Since I had heard there were many challenges around re-wiring an original harness for use with a modified PCM, I were prepared with spare PCM’s, Scan Tool and a SCT Flashing tool, prepared with tunes that would remove the PATS system ( the anti theft system that prevents a Motor from starting, if not started with the original PATS key.) I even had a Autotap Commander that would allow myself to re-program the original PCM. This is the Sniper hardware with PC software from Autotap. I also had a second PCM harness and a second Motor harness, and the donor car’s Wiring manual, so I were well prepared, including the skills from my work for living with Process control computers. With everything wired, and the battery mounted, and the PCM disconnected, the first test were to pull all fuses, and apply power, by connecting the positive, to look for sparks. It was no spark, so no short. Then with the fuses in one at a time, doing the same, still no sparks when connecting the battery voltage to the main harness. Now with the key in the IGN position, and touching the battery positive to set the harness alive, there were no wild fire sparks, so time were come to measure that I had supply voltage at the 3 power supply terminals on the PCM connector. Ground connections were already checked. The time for the big moment were arrived. Plug in the PCM, connect the battery, connect the Scan Tool and turn ignition on. At this stage I wanted to see water and air temp, and throttle position sensors basically working on the PC. This would be the test that the PCM is sort of operational. However, the Scan tool would not connect. What could the problem be ? The first thing that striked me, was that the PCM do not work. As I had multiple 1997 MarkVIII PCM’s , I disconnected power and replaced the PCM. Still the same. Now was time to check out the wiring of the DLC connector ( OBDII / diagnostic connector), but it appears to be correct wired according to the 1997 MarkVIII wiring manual.