Hard to tell in the photo but it does not seem correct for those two green wires to be connected to each other. I am wondering if the previous owner was trying to use the back up light as a second stop/turn. I make reproduction tail light lens for the 75 - 79 Nova and have had requests for some with a red lens in the back light position.
Your flasher appears to be an electronic unit, usually needed with low resistance circuits like LED lighting.