The reverse lights are in the trunk lid and they had a regular spade terminal for the ground wire to plug into. The tang on that socket does not look like a terminal. 1966-67 coronets have reverse lights in the bumper with power wore only, ground is through the lamp housing to the bumper.

Here a pic of an under dash courtesy lamp. 2 wires in the top. The tabs to hold it in the bracket look the same.