The throttle cable goes to the throttle body (if you look under the tank, you will see the cable) The TPS is mounted on the throttle body. When you twist the throttle, you can see the end at the throttle body rotating (which opens/closes the butterfly valve). Depending on the amount of throttle input (i.e. you twisting the throttle), the resistance in the TPS varies and the tps sends the signal to the ecu to manage ignition/fueling etc.
On a ride by wire system, there is no 'throttle cable' per se but probably a electric wire going to the actuator that will open & close the butterfly valve depending on the throttle input. So when you twist the throttle you are essentially varying the Voltage/Resistance and this signal is used to control the throttle body and probably the fueling/ignition..etc. (it may or may not have an additional tps)
Here is a very good explanation on the working of a RBW system:
CUT THE CABLE! | MOTORCYCLIST
I haven't seen the new D390 yet, so can't give you the exact layout/working of the rbw on it. The concept though is the same as explained.



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