I just picked up a set of aftermarket DPN tow mirrors second hand. My truck is a 14 Sierra 1500 SLT with DL3 mirrors. I know I'll need the RZY harness as well as your DIY door harnesses to get the marker lights and cargo lights to work but i have another issue. after installing the new mirrors, my turn signal will turn on both sides signals on the mirrors and in the headlights but not the tail lights on the bed.If I unplug either mirror, my signals work correctly on the other mirror and headlights. Could this be an incorrect pin layout in the connector?