In May 2016, under very similar facts, a New Jersey Appellate Court came to the same conclusion.(State v. Murphy). However, the N.J. Supreme Court seems to have overturned that decision, in a more recent case, State v. Scriven. In Scriven, an officer had stopped to check on an unoccupied vehicle, when he noticed another vehicle proceeding down the roadway with it's high beams activated. Believing this was a violation of the motor vehicle statutes, the officer stopped the vehicle and upon approaching the vehicle smelled marijuana. A subsequent search revealed marijuana and a handgun. In this case the officer was also wrong about the high beam statute, that only requires drivers to turn them off when they're approaching other vehicles, and no other vehicles were on the roadway when the Defendant was driving with his high beams on. Here the Court found the officer's mistake of the law unreasonable. Frankly, I don't see the difference between the two cases, both officers were wrong about the law, and one didn't seem more unreasonable than the other. Since this was decided by the State Supreme Court, it seems to help Defendants. However, for future cases like these, where both officers believed the Statute they were enforcing said something different, how are courts going to decide whats a reasonable mistake of the law?
The police need reasonable suspicion that you have either committed or are committing an offense, before they can stop you. If they don't, the stop and any arrest, or evidence they seize can be suppressed.