I have never come across anything except a police department policy that requires a cop to identify himself to a traffic stopped driver. No law or anything like that.
I s'pose that's why many cops wear uniforms and badges. In court opinions I have come across references to people submitting to a "show of authority" mainly in cases where there was some discussion about whether the person was seized or not for the purposes of the 4th Amendment.
There are statutes like the traffic statutes that say a driver has to pull over and stop if a police car turns on his flashing lights.
Beyond that, I haven't come across such.
Please elaborate on what you are thinking as far as cooperation. Are you thinking "at what point am I compelled to submit to the cops authority?" Or, are you thinking, "How identity info does he have to give me before I help him investigate a crime by another person?"