Hi. I have a 2004 Impala that used to be a police car. It was the 9C3 undercover package. Yesterday, my left turn signal started blinking very fast when I would turn it on. The front blinker is still working, although it is blinking very fast. The rear blinker was not working. I changed the bulb, even though the old one didn't look bad. It didn't work. The bulb still lights up for other things, but it won't flash when I turn the turn signal on or when I turn the emergency flashers on. I'm not sure where to start looking next. Can anyone point me in the right direction?