The company I works for manufactures LED motorcycle lights (what a pity, only in VietNam) as well as modulators.
We advise the modulators is inserted in the HIGH BEAM since it is, usually, the least used headlight filament.
WATCH OUT when using COLOURED LEDs! Coloured LEDs are very specific in their light frequency and often a 'red' (colour temperature not specified) will not work with well with a coloured lamp cover. You are far better off using a WHITE LED (which is also actually slightly coloured) as the light level emitted beyond the lamp lens cover will be greater.
Naturally, working for an electronics company, meant I switched 100% sides, tails and turns to LED - so no Plod/Cop can claim your tail light is out.
Aftermarket headlight conversions usually fail as the reflectors are designed for a single light source rather than multiple LED light sources. I add a lower power laser to my headlight to 'spice up' the light level. Unfocused lasers are not harmful to eyes when viewed at normal distances.