What is the law? (can a cop do this?)
Reply #1 –
If they are enforcing actual laws of sound from the car and proper function of lights, they can enforce it. It may seem nit picky, but, if it's the law, that is what the cops are hired to do...enforce those laws.
As far as ordering a person into their car after they stop you, yes, it's for the officer's safety. They never know what people are going to do. You are honest, but they may not know that, and they can't just take a person's word for it.
I was a police officer some years ago. I wasn't quite as picky, but, I did have to pull people over at times for bad lights and such. Burned out lights are a danger at night. You may be able to see, but it's also about people seeing you.
I can't say I always agree with the way police do what they do, but I also have seen it from the other side, and understand where they are coming from.
If you are stopped that often, just make sure your vehicles are up to the legal standards and then you won't have to worry.