HAVING SAID THAT; there is the possibility that this is caused by a bias current generated when the asymmetrical electrical noise generated by the horn is rectified by the diode (LED). Of course, one way to know would be to disconnect the horn - press the button - and see if the highbeam indicator glows.
I have experienced similar symptoms with LED lights on my Moto Guzzi, I was advised to insert a diode in the ground leg of it to fix it, It did fix it. Seems to have something to do with voltage bleed if memory serves me correctly.
Interesting ! A diode in the ground wire of LED will stop any stray current reaching LED bulb since diode conducts electricity in one direction only. It must be connected with correct orientation / polarity.
Strangely, the LED warning bulb is itself a diode, so I'm not sure what difference adding another one would make. (Actually you can get bidirectional LED bulbs, but I don't think they are common. I had to make the one for my flasher warning bulb.)
@ SinghThis happens on my bike as well. Another thing that happens is when I use the indicators, the headlight also dims just a tad in sync with the indicators flashing It is happening since I bought the bike. The issue(s) are not that serious enough to warrant a checkover (For me)
singhg5- The diode was a basic axial lead style from Radio Shack (it looks like a low wattage resistor) the cost was about 5 for $0.50 ten years ago. It has been at least 10 years ago but I think the positive lead connected to the LED.
LED bulbs in my bike are bi-directional and work with AC or DC.Did you notice this on the OEM incandescent bulbs OR after changing over to LED bulbs ?Yeah, there is nothing REally wrong with it, just CURIOUS MINDS WANT TO KNOW - If Arizoni doesn't mind me using his phrase !You were 10 years ahead ! We are gradually catching up at a leisurely RE pace .