The first light that I ordered did not work at all when I received it. I put in a new bulb and it worked with the brake lights only, and not the tail lights. I  called Bully and they said it should also work when the lights come on and get brighter when you apply the brakes. I sent the light back to Amazon and another light was sent. The new light only works when the brakes are applied also. I still have the 2nd light and I do not think I could have received two defective lights in a row. It just does not work as the manufacturer claims that it should. I'm disappointed.