New LED tail lights 69 Cuda

Here's a clearer explanation:
USDOT does not certify anyone or anything. The manufacturer or importer of a vehicle or regulated piece of equipment is the party who certifies that the vehicle or equipment meets all applicable provisions of all applicable requirements. There is no requirement for any particular testing or other procedure before such certification is made, but the certification comes with full legal liability. It is entirely up to the manufacturer or importer to do whatever testing will satisfy himself that the device or vehicle actually meets the requirements. It is a self-certification regulatory regime in North America, and always has been.

If reason arises to believe a particular vehicle or piece of regulated vehicle equipment is not in compliance -- usually "reason" means injuries, deaths, newsworthy crashes, or consumer complaints -- USDOT may purchase and test samples of the vehicle or equipment in question. If noncompliance is found, they can order the manufacturer or importer to recall and repair or replace the noncompliant equipment, or in the case of aftermarket parts, repair or replace or refund it. They can also levy substantial civil penalties in the form of fines.