So I've finally gotten around to another 3500 swap on my latest 97 Cavalier, I have found a harness that will work 100 percent of the instrument cluster. No BS.. Tach, temperature, A/C compressor signal, oil pressure, battery, vehicle speed, check engine, and even the factory theft system.. Yes, I said it, the factory theft system.. Since I live in California, I'm making this car smog legal so everything needs to function. Here's what vehicles will work for the correct PCM and engine harness to use..
-1998 Oldsmobile Achieva 3100-
-1998 Buick Skylark 3100-
-1998 Pontiac Grand Am 3100-
Only the 1998 PCM and harness will work, no 1997 vehicles or 1999 vehicles will work for this. Also the 1998 PCM is supported by HP Tuners.
I also compared pids from my Snap-On scanner to what readings are showing on the cluster and all are accurate.