Thanks, that makes sense. I'm thinking about replicating it but hooking up that y to the usb port in the console using another harness. Have you tried that?
I'll probably have everything out tomorrow to take pictures of the joycon because I just found out that I have to self isolate for 14 days because a coworker had symptoms. Also I forgot to hook up my ac controls a few days ago when I was messing around with things, haha.
Until then here's a picture I found on my phone that has most of the information I think you'd need. My car has the bose system and no navigation. Pin 6 and 16 went to channel A and B respectively although it shouldn't matter. I grounded the joycon ground wires for channels A and B as well as pin 15 from the Metra harness to the same bolt I used for the mk1 electronics.
Let me know if there's something more specific you want a picture of for when I have it out tomorrow.
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