I have a 2006 Cobalt. Drivers side tail light does not work. Turn signal works, brake light works, bulb is good. Put in new pigtail, same problem. Passenger side is fine. Traced wires through trunk to back seat, no noticable problems. Recently had heater core replaced. Could it be a loose wire under dash due to removal of dash when replacing heater core? Looking for help troubleshooting this to avoid going to dealer. Thanks