Yes well the clock harness is likely used by the nav harness.
Just as nav brightness mode has three positions and the clock has two, it’s probably your clue to switching between night and day mode on the roll switch.
Indeed using the FSM (for clock) wiring and pinout diagrams and or the nav service manual pinouts will give you a good idea as to the control schema.
I’m certainly going to get around to looking it up just for fun.
Due to the variable ground scenario that’s used in some gen4 circuits, it’s likely that some trickery like a diode or resistor is required to send the right signal.
There’s clues as to the year and model clocks as well. They’re either 3 or 4 button, the latter with Bright button.
So what year is your H6?
As stock did the car have nav, or what type of clock?
If it had a cubby clock, was it 3 or 4 button and what was the fuel consumption readout, eg km/100 or l/km etc?
Also if you get stuck, svxdc on lgt forum is an absolute genius at this stuff.
Additionally there’s yahoo jp vendors that supply all sorts of related harnesses etc.
Kenwood oem nav service manual:
https://www.dropbox.com/s/dpu1d0sn2pa0m ... 7.pdf?dl=0