Engine numbers will be on a pad right under where the variator is below the side cover.
https://donutpros.com/blog/gy6-engine-code
As for the harness, the few buggies I've messed with so far it was just easier to trash the hacked up harness and start over. A. the harnesses on them at best are junk B. too many times people try to "fix" the junk harness making it even bigger junk. Maybe this will help
