Question: I was recently in a car wreck where I rear-ended someone. However, their brake lights were not working. I thought the car was moving, but it turns out it was stopped. Am I still liable?
Answer: Just the fact that the vehicle had an expired inspection sticker is not a defense. That fact alone would probably be inadmissible because it is usually irrelevant to the accident. However, if you can prove that there was something wrong with the vehicle that contributed to the accident, then it becomes relevant and more likely to be admitted into evidence.
In your case, if you can prove that the brake lights were not working and that the inspection sticker was expired, then the expired sticker becomes relevant since it helps explain the events leading up to the accident.
The issue now becomes whether your testimony alone is sufficient to admit the expired inspection sticker into evidence. My opinion is that it is sufficient. If your testimony is facially credible, then I think you are entitled to use this evidence in your defense. Some judges, however, might want something more (like an independent witness or admission of the other driver) before admitting the expired sticker into evidence. Otherwise, there is a potential for people to fabricate such matters in order to get otherwise inadmissible evidence into the case.