Well, Wal-mart certainly wouldn't be able to fire you if you called OSHA and reported those unsafe conditions, would they? The thing is, if you want to call OSHA and report this unsafe situation, they won't tell the dealership WHO called in on them, though they may be able to guess, since you have had such issues with falling lights.
You seem to believe though, that there should be a bureau of something that would come in and make the dealership fix the lights, reimburse you for damages and mental anguish, even though the dealership isn't even your actual employer. But frankly, other than reporting them to OSHA, there's nothing you could do, since you really haven't had any real damages, it's all just potential, man, I could really really have been hurt there, you know?
If there were any damages to your car, you could probably take the dealership to small claims court if they refused to reimburse you for the damages to your vehicle. (And your actual employer, the detailing company could certainly fire you for hassling their customer, and you'd have no real recourse there except MAYBE unemployment insurance. You are not a whistleblower. )
And the judge could question why you were in there cleaning your personal vehicle, was that really appropriate since you already had had a bad experience with falling lights and knew it was a dangerous place.