No Tail Lights or Rear Side Marker Lights

[gschroeder]

I have a freshly restored 1970 C10 with tail lights and rear side marker lights not working. Brake lights work, and turn signals work, but no tail lights or rear side marker lights. I confirmed with a test light there there is power coming to the tail light and side marker light socket. Side marker light grounds are hooked up, and bed is grounded to the frame. I tried using the test light as a temporary ground, but still could not get the tail lights or rear side marker lights to work. Any suggestions on what to do? Thank you for your help. Thank you