He forgot to fix his car's rear stoplights, so he needs to be extra careful when driving at night.

stoplights 是由 stop（停止）和 lights（灯）组成的复合词，指"刹车灯"或"停车灯"，安装在车辆尾部，当踩刹车时会亮起红色灯光，提醒后方车辆注意减速。 rear 在这里是形容词，表示"后部的、尾部的"，用来修饰 stoplights，所以 rear stoplights 特指"车尾的刹车灯"。