Professional :: Police Car Drives Along With Flashing Lights In A Scene ?

What is correct way of creating a police car with flashing blue lights drive along in a scene?My plan was to create a new file, add car and png of just the lights to the library.layer 1 rename as car and dragdrop car graphic to stage, add keyframe at fr48 for 24fps scene, 2secs duration insert a layer call it lights and drag drop to stage, make duration 24frames, lights flash at 1 sec intervals when movie played.Should I select both layers and go modify>convert to symbol>movieclip then copy paste that from library to the library of the scene with the road ?(it doesnt flash !)How is this done ?

I also presume the fps of the movie clip if taken to another file should be the same as that file, one cannot have movie clips of different fps in one file, am I right ?