CEL always on, or always off...

[Sea Aych]

So this isn't the standard "my stomp test doesn't work" or "why is my CEL on" question...

For context my car is 5spd swapped, and was previously a euro automatic, meaning it had the 4HP22-EH transmission and the 6-pin, round TPS.

What's going on:

• Car starts and runs perfectly, but the CEL just stays on all the time, and the stomp test does nothing.
• TPS registers WOT and closed without issue.
• Unplugging the transmission computer turns off the CEL, but all the time. IE when the key is in the "on" position but the car isn't running, no CEL.

First on my list this weekend is to try and rip out all of the leftover transmission wiring because something is obviously still connected, but am wondering if anyone else has run into this issue before?

[Sea Aych]

So interesting developments after doing some digging the past few days:

1. There is no pin wire in my C101's Pin 12, on the body side. The car is 100% original wiring, which is what makes this even stranger. Engine harness has pin 12 wired in. It turns out that many euro/japanese models, especially the earlier ones, don't have the check engine light at all.
2. The CEL in the cluster is fed from a wire that runs directly back to the trunk's TCU for the EH transmission, along with the wire plugged into the odometer.
3. There's no trace of the "standard" E30 wires to replace either of these, that I can find. I'm hesitant to tear into the wire wrappings for the body-side stuff.

TL;DR It seems like cars with the "selector knob" and the 4HP22-EH trans, aren't perfectly plug and play for a manual swap, if you're expecting CEL functionality.

Next i'm going to see if any of the rest of the transmission harness is plugged or spliced into the body harness anywhere else past what we usually know.