There's a bunch of other wiring here I just won't be using at all - cruise control and airbag.
The issue here it the large connector block at lower left - it conflicts with the adapter that the new wheel bolts to. The yellow wiring is for the airbag, so I just cut that away entirely, and then I removed the plastic shroud around the four other pins - even though I only need two of them for the horn.
I'm going to keep a box of all the excess wiring I remove from the donor harnesses. This car is going so have so many fewer switches and buttons in it than the donor that I should be able to remove some real weight.