I don't know about your tack/volt meter but when I installed the LED volt meter that was being sold by Kevin Mahoneys company that imported Royal Enfields, I wired it to the gray wire in the headlight casquette that powers the headlight parking light.
Since I removed the wiring jumper that keeps the headlight on, my light switch now can turn the headlight on or off.
If I start the engine with the headlight turned off, a quick glance at my LED volt guage shows me it is not lit up.
That's a good reminder for me to turn the headlight on before riding off.