Actually look in the FEDERAL motor vehicle safety code. (FMVSS No. 108). Back when I built conversions, we found out that it is illegal to install HID's in non-oem hid equipped vehicles. Nothing to do with states regs, just federal. But if HID's were available as an option on the model, we could install factory HIDs on them.
Erroneous! Erroneous! Erroneous on both counts!
FMVSS108 does not bar the installation of HID headlights, so long as the lights meet the chromaticity and photometry requirements outlined in 108. There is no explicit prohibition on installing those lights at all contained in that regulation.
This whole thing is misunderstanding caused by not reading carefully enough, and not understanding that NHSTA letters of interpretation ARE NOT LAW. They have NO legal force. Back on '03, the agency sent a letter opining
that a plug n' play HID bulb conversion was not in compliance because that bulb was not designed for that reflector housing, which would cause the beam to be out of spec as far as the angles and such.(as many of you know, putting an HID bulb in reflector housing throws light all over the place.) It did not speak to full headlight unit replacement. From that, the big game of internet 'telephone' distorted the letter's content and importance.
Furthermore, the FMVSS has issued a letter of reconsideration of that '03 letter, since it became obvious that people completely misunderstood it.
In relevant part, the FMVSS's letter of interpretation dated NOv. 1 2005 states
source: Federal Register
This language is relatively straightforward. For any particular
item of lighting equipment, e.g., a lamp, FMVSS No. 108 states only
that if a lamp is manufactured to replace a lamp on a vehicle to which
the standard applies, it must be designed to conform to the standard.
It does not say anything about the replacement lamp's being required to
have the same type of light source as the OE lamp. Moreover, while it
is true that, unlike other lamps, FMVSS No. 108 specifically regulates
headlamp systems including their light sources, neither the language of
S5.8.1 nor any other language in the standard requires replacement
headlamps to use the same light sources as the OE headlamps.
FMVSS 108 doesn't say they're illegal, and now there is a letter of interp stating what should have been clear from reading the reg (instead of internet chatter) in the first place.
Case closed. Never send a cop/headlight maker/consultant to do a lawyer's job.