Steering wheel audio contorols - Yaris 2003

[BXN]

Originally Posted by CTScott

Yes. The spiral cable ideally has more wires in it when the steering wheel controls are present, so the difference between those two part numbers is likely the presence of those extra wires.

I already know about that (mentioned that as an opening to my post and because I think that could be the reason why levvy coundn't make his switch work with radio).
I was asking "Are there other elements that determine is it possible to use STEERING AUDIO SWITCH?", because as I looked in parts catalog and service manual, I couldn't find any other parts associated with audio that had 2 versions (with SW support and without).