I used the BlendMount/MirrorTap on my 2021; + is the mauve/purple and - is the black with the white stripe.
To clarify, I'm using the plug at the very bottom of the area covered by the mirror/windshield housing. I'm also using the vehicle end of the plug, rather than the end that goes to the mirror and associated equipment. Works flawlessly and powers up with the vehicle.
The mirror taps have worked well for me in this and prior vehicles, but that custom harness looks promising. The BlendMount mount is a game-changer though over suction cups or adhesive.
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