So, this story begins with getting pulled over the other morning for running without lights (unbeknownst to me.) My 2007 Impala LT 3.9L's parking/marker lights aren't working. I've changed the bulbs. It's both Left and Right rear marker/parking lights. Both Brake lights, turn signals, and reverse lights are functional. What could be causing this issue. Thanks in advance for any info anyone can provide.