Did you happen to look at the cables? I have seen perfectly lookiing cables that were eat up on the inside.
We have to crawl before we walk, even I have to take a step back sometimes from a fix cause it was a SIMPLE fix and I over complicated it.
Also iof the cables check out fine.
Next I would pull the gauge cluster out and verify that there is no corrosion on those pins either.
Sometimes just removing the cluster and installing back FIXES this.
Other times I had to get contact cleaner and clean the pins both on the cluster and the harness.
If that dont get it going
Take each connector off the computer and look at the pins. I had one pin that was corroded and it gave me fits fixing that.
Even if all the pins look good pop the back off that connector and look at the back of pins. thats where my issue was. I just spliced a new wire and pin in and was good.