49 U.S.C. § 30145

Section 30112(a) of this title does not apply to a motor vehicle or motor vehicle equipment if the vehicle or equipment— (1) requires further manufacturing to perform its intended function as decided under regulations prescribed by the Secretary of Transportation; and (2) is accompanied at the time of importation by a written statement issued by the manufacturer indicating the applicable motor vehicle safety standard prescribed under this chapter with which it does not comply.