SS,MkIV tail light / number plate housing

Going by the wiring diagrams for 39-47 SS/MkIV’s there is a variety of combinations for reverse / tail / stop light positions.
I have established that the reverse light is on the nearside (left) of my MY40 SS saloon however I cant establish which way around to install the box assembly as it only has the bulb holders and no wiring colours for identification.
It is not mirror imaged as one long edge on the backside is tapered and the other side edge is flat.
So my question is are the bulbs facing up or down? and / or is the taper at the top or bottom?
Thanks in advance.

On my '38 the bulb glass is up and the brass socket is down. The wire clips are along the bottom.

I live in a high traffic area, so in the interest of rearward safety, I made both sides reverse and tail, and added outboard tail and brake lights.

Thanks for the excellent photos.
Is the bottom of the box tapered and the top flat?

Which way is up?

I see you have a clear lenses each end?

Ah, I see the difficulty now. Your cover and sockets seems to be reversed from mine relative to the back piece.
Yes, on mine the tapered side is on the bottom, as are the metal clips that hold the wiring. I suspect it is tapered to prevent water retention.
I chose to have two reverse lights again for safety in parking lots, two white lights being the universal signal that a car is backing out of a parking space. Plus one reverse light and one brake light is unsymmetrical and looks odd. :grin:

Thanks Rob.
My assembly looks to have been repaired in the past and quite possibly have been reassembled incorrectly.
The key thing is I need to ensure is I have the lenses covers with the retaining screw at 12 o’clock position.

Rob. Have you wired your brake light and tail lights to twin filament bulbs?

I think you meant the lens cover screws are at 3 and 9, but anyway be sure the wire that holds them in is good, so they don’t fall out.
I left the original bulbs singles, as I decided that as brake lights they really weren’t very effective, especially in modern traffic. My additional lights on the bumper are twin filament and pretty bright when they say STOP. I decided I needed a non-invasive period-accessory way of reducing the chance of a rear-ender.
I’m not the only one. Notice this Bentley owner had the same idea.

Yes, mine too.


Thanks Rob and Peter.
Rob. I now understand what you did with your brake lights.
Can I have a closer photo of the assembly installed. Is there a seal?
Cheers, Graham

Yes, there was a seal around the unit. Mine was like a thin wall tube, pretty well shot, so I chose to use a length of vacuum hose, glued around the edge. It’s not a perfect fit, another possible case of this being one of the first cars to have a spare tire door and things didn’t fit together all that well.