Ok....... this is my RHD kouki build
https://instagram.com/sushihadmelike/
Its ALL oem harnesses uncut etc. No cut firewall.
I have 3 clusters, 2 USDM one JDM, I was curious one day to see if my USDM cluster just plugs and play and hey guess what? It did.
I plugged my zenki cluster, kouki cluster, and jdm kouki cluster and they all work perfectly fine. So why do your plugs not work? I don't know maybe you have the wrong harness?
The only noticeable difference was the MPH were 4 miles higher than what I was going (tested it with GPS on my phone).