V5 Solenoid cable

I am looking at the v5 solenoid cable that goes from the brain to the solenoid itself. Does anyone know how the cable works as in the wiring or how does it go from 3 wires to 2 wires. I’m wondering if anyone knows how the wiring works in the black knob thing in the center.


Have a look at this old topic, there’s a conceptual schematic half way through the first post.