New LED tail lights 69 Cuda

There are no actual laws as to what a light should or should not be.

That is not correct. Federal Motor Vehicle Safety Standard 108 is a Federal law, which contains mandatory design, construction, performance and durability requirements for all regulated lamps and reflective devices, including stop lamps, tail lamps, reversing lamps, etc.

We did however, based on SAE standards, test photo-metrics and similar practices

Some aspects of current and past SAE standards are incorporated in FMVSS 108 requirements. However, SAE standards themselves do not carry force of law. Compliance with SAE standards by itself is not sufficient to demonstrate legal compliance of the product; for that you must certify compliance with FMVSS 108.

With any custom or non-OEM product, it is ultimately the user’s responsibility to use them in the appropriate way.

That is not correct; the responsibility and the liability is yours as the manufacturer. Under Federal law, each and any regulated item of vehicle equipment must be certified by its manufacturer or importer as fully complying with all applicable provisions of all applicable Federal Motor Vehicle Safety Standards if it is physically capable of being installed on a vehicle certified by its manufacturer as compliant with all applicable Federal Motor Vehicle Safety Standards. All vehicles made on or after 1/1/68 for sale in the United States market are so certified; prior to that date no Federal Motor Vehicle Safety Standards existed.

I can gladly provide a light and you may engage in any test you feel would satisfy your fulfillment.

That would be interesting, but the responsibility to do (and pay for) those tests is yours, not mine.

You make strong and intimidating claims, without warranted proof

Nonsense. You seem not to understand your responsibilities and obligations as a manufacturer of regulated vehicle safety equipment. Federal Motor Vehicle Safety Standards are promulgated and administered by the National Highway Traffic Safety Administration, an agency under the Federal Department of Transportation. I provided a link to NHTSA's information sheet on the responsibilities and obligations of importers and manufacturers of regulated vehicle equipment. Did you read it?

to quickly render our product useless, below original standards, and question our intention and work.

I asked you a simple question: Do you certify your product as compliant with all applicable provisions of Federal Motor Vehicle Safety Standard 108? So far you haven't answered; I have to asssume, then, that the answer is "No".

Want to do it right? Get in touch with Calcoast ITL. They're a reputable compliance testing lab, and they'll happily spend time on the phone explaining your obligations under Federal law, even if you choose not to go forward with their testing services.

Frankly you're acting like an all-mighty douche

You're welcome to your opinion of me. The law is the law and your obligations under it are your obligations under it even if you choose to ignore it. If it gets you to bring your product and compliance in line with the law, then you'll probably wind up sooner or later thanking me for saving you from a ruinously expensive liability lawsuit and/or civil penalties from NHTSA.