The rear tail lights light-up in a dimmer seting when you turn the headlights/marker lights on. First turn the lights on and see if all of them are working in the marker light seting. Then have a friend step on the brake petal all the the rear lights should be BRIGHT and the high mount stop light in the middle of the rear window should also light-up!! if any do not replace teh bulb and you are good to go!!