I think headlights are required by law when it's raining, in most of the US but I'm not sure :P
Since it's common for mods to have no headlights now, can I suggest using the "centre" brakelight dummy for the back lights instead of "right/left" brakelight? Otherwise the back lights will be on at all times but the front ones won't, kinda weird. I know some mods already don't have neither front nor rear lights on which is alright.
As an alternative, for a car I converted once I tried extending (scaling) the normals of the headlight models (and also using the headlightreflector material) so they always look brighter like they are on, not sure if it's a good idea: