You remember I said primitive right? The hole has a rubber grommet. Lower section of housing has a copper strip going down near a "L" bracket/strip of spring beryllium copper. Which has a phenolic insulator on the top side and a hole for the bulb contact to stick thru. The bulb base is grounded by touching the bottom side of the "L" bracket. You wedge the bulb between the grommet and the "L" strip. Which pushes the "L" strip and the bulb contact up against the copper strip, which is connected to the second wire terminal.
I am going by what I see in pics. Don't have a light to look at in my hand but that is close to how it works.
NOT WORTH TWO CENTS TO HAVE AS A TRUSTED BRAKE-TAIL-TURN rear light. Especially now that it is Chinese.
I advise a light like the ones you are probably taking off. It's a military troop carrier, who knows what it had on the back.
If you must have the look, you will need to modify the housing with a "modern" dual bulb socket, as you said earlier. I could do it but it would be semi-pricey.
I have asked you if you have instruction and you did not answer. I asked if the right side had a hole in the bottom, didn't get that answer either. You pic is cut off at the bottom. I asked for all kinds of more pics. Didn't get those either. Are you reading our responses? Do you want help or not?
I see the one you have has the copper strip going down to the lower area. It also has a insulator. I am guessing that on the underside, which I can't see, there is a hole in the insulator for the lower bulb contact to touch the copper strip. I don't see how the bulb base gets grounded unless that other piece that I said is and insulator is actually metal so that the base touches it and gets grounded. I think it's still a "wedge" the bulb situation down there. Maybe you have an extra part floating around the box. AGAIN, better pics and any instructions you received would help.
