Tying threads together. I'm working on the DIY approach myself, and ran into the same issue as
@danlatlanl above. Here's that thread:
Retrospective thread-summary pseudo-wiki for quick access: What is it? "Gee, I wish my Tesla, despite having access to the country's biggest quick charging network, could also charge on stations made for Other EVs too". Said no-one ever. Except... well, there are use cases for it. And with Tesla...
teslamotorsclub.com
Prognosis so far isn't great. Just discovered today that there are differences in which pins are populated, and there also appears to be at least two different revisions of the entire charge port assembly in the car. This worries me, a fair bit.
When I had the Gen4 installed, I had "CCS adapter support: enabled" in the additional info display... but I also had a mess of charge port faults. In particular, CP_a009_coverOpen (described as "position not detected, can't be determined if closed") and CP_a109_thermistorIrrational (described as basically "there's a missing thermistor so can't determine port temperature"). Makes sense if the ECU has physically different pins populated, and a wire present in the connector lands on nothing, and a pin on the ECU goes to no wire.
Huge bummer, but this may be why the CCS adapter hasn't come to NA yet -- cars in the target Korean market are all >2020, so they all have the Gen4 and new harness already, no need for any ECU swaps for supported cars. For us, they may still be developing the retrofit so they can offer it all together. Hopefully that's the case.
For me, though: oh well, it was a $150 ECU and I can easily toss it on eBay and sell it in minutes.