Classic/Antique Car Repair: 1967 Impala rear lights not working with headlights, ground connections, promblem

Question
I have a 1967 Impala Fastback. When I turn on the headlights my rear lights dont come on, and if i hit the left or right blinker they dont work and the arrow in the dash remains lit and dosent flash. If I turn off the head lights my right and left blinker operate fine. My back up light dosent operate either. I replaced the bulbs and checked my fuses(all good). I even bought a used wiring harness on ebay and i am having the same exact promblem.

Answer
Phillip, the first thing that I would check is the ground connections for the rear lights. That means all the way back to the battery. If the ground wires are attached to the bumper or bumper back bars the connection to the cars body could have rust between it and the body. The directional lights, running one bulb, requires less current than the full set of tail lights and that explains why they work when the head lights are off. Good luck.
Brad