LE procedure for search/harassment

florida. tested completely negative at a roadblock stop for alcohol. Then, informed that a "mechanical inspection" of the car would occur. Car tag light was determined to be out. Held 40 minutes until cited for tag light. Informed that computer delay was the hold up. (pardon the pun) Evidently, they were running a make on the license and tag number. Polite demeanor used throughout. Designated alcohol roadblocks are legal of course. But is there case law to allow "mechanical inspection" , without any probable cause of an infraction?

You call them on it and I can guarantee that there going to come with with a legit probable cause. Something as minor as that ain't worth the time and effort to mess with. That's why the get away with the crap