Cruise control fitting - light comes on dash but not slowing vehicle

2010 prius (right hand drive model)

Hey guys, I had to replace my indicator stick recently, and in the process decided to also retrofit a cruise control lever, since I had to completely remove the steering wheel anyway. Installation was/is pretty easy (for anyone else considering it), but, ALL of the pinouts suggested in any videos/images for the installation I could find are already populated with other wires already. The vehicle (previously) had automatic parking installed, before my dealer replaced the head unit with something a little more useful (original was the big screen Japanese model with navigation/Bluetooth)

I still plugged everything else in (into the slot already existing in the wheel), and while the light comes on in the dashboard and shows set status when set, it doesn't actually impact the vehicle in any way.

I'll take some photos of the ECM (if that's the right term) under the dash when I can.

Mostly what I'm asking is where should I be plugging it in? It's a Japanese import model. (ZVW30 I think) I've tried checking the service guide but it's not really clear at a level I understand.