You should sit down with local counsel to discuss the myriad of ways that a false positive can register on an IID prior to writing anything.
No answer here should be considered to form an attorney-client relationship. You should consult with a licensed attorney in your jurisdiction so that a full evaluation of the facts of your case can be conducted.
I assume the letter the SOS has requested must be given under oath or verification. Your answer must therefore be truthful. If it was truly a false positive, simply explain that you do not know how it happened and affirm that you did not consume any alcohol on the date in question. If you know you consumed alcohol, you should speak to your attorney that handled your DUI before sending in any letter. Not only may the consumption of alcohol trigger an explanation letter to the Secretary of State, you were in all likelihood ordered not to consume any alcohol prior to driving during your term of supervision or probation. No need in sending a letter admitting you violated the terms of your supervision and/or probation. Talk to your attorney, it is worth the money!
This response is being provided for information purposes only and does not constitute an attorney client relationship. Furthermore, I am only licensed to practice law in the State of Illinois. While there are oftentimes similarities between States' laws, there can also be large differences. You should not rely on this response as legal advice and are highly encouraged to speak to an attorney licensed in your State for an accurate legal answer.
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