OP
I traced the wire and it's grounded. I just ordered a new IC programmed to my VIN and miles. If that doesn't fix it I'll move to the wiring harness. I'm not good with electrical and don't know anyone with a TJ. Just bought this and the check engine light never worked. I usually just look to see if it's not on.You followed the Black with Light Green wire from the connectors to that "dead end"? One way to make sure the IC ground is good it to check resistance or continuity between the Black and Light Green wire and the chassis. If it shows open then that might be the issue as both the Check Engine and Check Gauge lights as illuminated by being grounded VIA a transistor in the IC circuitry. If that ground is missing the light cannot illuminate.
IF the ground is good then it seems to be pointing to an IC issue, have the Check Engine and Check Gauge lights ever worked since you have owned it?
I would hate to spend ~100.00 bucks on an IC and that not be the problem. Do you know of someone that has a similar jeep you could swap IC's with to see if the light work?