[marc]

In the canbus system the the tail light gets 6vdc, when you apply the brake the canbus sends 12vdc to make it brighter.

That is not quite correct. First, not all CAN bus bikes use the same scheme. Second, the scheme used is called pulse width modulation. The effective voltage may be on the order of 6 and 12 volts (don't know the actual numbers) but the the actual voltage is always the 12-14 volts that is standard for your bike. The 12-14 volts is modulated on and off to give you the lower effective voltage. You'd need an oscilloscope to see this.

 

[marc]

From the GS wiring diagrams it appears that the only real CAN
communication is between the engine computer (BMS-K) and the
body computer (ZFE)

And the COMBI (Instrument Panel Controller). The optional ABS controller, Alarm module, and tire pressure modules are also attached to the CAN bus. As you noted Lights, switches, and sensors are direct connected to one of the various controllers and have nothing to do with the CAN bus.