I have same problem with the S2 LED headlight I bought from Motominded, it flashes on for 1/2 second then nothing, no light.
If I turn off the bike key switch, wait 10 sec, turn it back on, LED flashes again, then dead.
Here's a portion of the prompt and detailed response I got from Motominded:
The AUX circuit we plug the headlight and harness into has a minimum and maximum load or the computer shuts the circuit off.
Alta will not tell us what the minimum is. We are guessing about 5 watts. If the computer does not see the load, the circuit shuts off.
Alta told us the maximum is 4 amps. We know this is not true because we tested with a Squadron Pro at 3.5 amps and the circuit shuts off. I am successfully running the Ultimate Kit, with tail light and it is pulling 2.8 amps and works fine. We know the upper limit is somewhere between 2.8 and 3.5 amps.
Your LED is pulling .9 amps. or 12 watts. Safe within out tested range.
I called my Alta rep and he is looking into it.
I do not understand why they would have a feature that turns off a circuit if a minimum amperage is not met. Maybe a safeguard?
Apparently most owners have no problems with LED lighting they fit to bike, but Wnuudiction and I are not lucky on this one.
In any event I will keep y'all posted if I learn of a fix.