I think it is for the light Illuminating the gear selector, and the two side lights on the console.66-70 B body. However, some years the color of the wires changed.
Do you have the harness that connect this to the dash harness? If so what connector does it have?
That would be for after 1968.... '68 and prior had the back up switch mounted on the console shifter mechanism, thus the 6 prong plug in Moparmarks picture. '69 and after, the back up switch was integrated through the neutral safety switch, thus 2 less prongs. That doesn't look aftermarket, it's identical to the one in my '69 bird.