Willtill - there is a popular misconception that modulators are only allowed on the high beam. That is incorrect - here is the pertinent language extracted from from the Federal Motor Vehicle Safety Standards, 49 CFR Parts 571 [Docket No. 97-57; Notice1] Executive Order 12866
Motorcycle Headlamp Modulation System
a.7.9.1 A headlamp on a motorcycle may be wired to either the upper or the lower beam from its maximum intensity to a lesser intensity provided that: (the rest of the section deals with the actual specifications that the modulator must meet).
Point is, it can go on either high or low beam, but must meet the frequency and intensity cycle requirements AND cease modulation when the light level is less than 270 lux (again, from the language provided in 49 CFR Parts 571.
My setup meets the requirements, it is sensor driven and the low beams remain fully functional should the sensor fail (just like if wired to the high beams). I added the cut-out switch for flexibility in case I want to turn off the modulation during the day, but since the normal function is to modulate during the day the switch is not really required.
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