He is talking about a license plate light,,,,the single pole would need to ground through the mounting screws and either have a ground strap to tailgate or rely on surface contact at the hinges or limit straps... SO the question is did 66 broncos USE a single pole?? the 2 pole sockets ran 2 wires down and out tailgate near the left rear body mount ground wire was atatched to body at body mount bracket and power wire went into harness mine had a bullet connector ,,