Looked at the Crutchfield page and the adaptor does connect to a single wire.
Compatible Aftermarket Head Units: The PAC SWI-RC Steering Wheel Control Interface is compatible with the following steering wheel remote ready aftermarket head units.
Alpine, Clarion, Dual, Jensen Pioneer, Sony, and Valor: The aftermarket head unit must be equipped with a 3.5mm steering wheel input jack.
JVC & Kenwood: The aftermarket head unit must be equipped with a blue/yellow steering wheel input wire. (Not compatible with Kenwood KDC-BT318U, KDC-BT558U, KDC-BT562U, KDC-BT758HD, KDC-X598, KDC-X798, KMR-D558BT, or KMR-D562BT.)
https://www.crutchfield.com/p_541SWIRC/ ... ml?tp=3405
This is so weird! One wire, why do we even need an adapter?