This thing came to mind as a better solution for reverse lights + fog light on the Ford Focus MK1 (also works on MK2 pre-facelift). I designed it, printed it, built it and tested it.

You will need a LHD and RHD reverse light for the Focus, some LEDs, resistors, FLRY wires and a bit of patience. I made it with 6x 5mm LEDs and 6x 3mm LEDs, warm white and red. You can opt for cool white LEDs or even just add more 3mm LEDs. I made a wiring harness out of FLRY automotive grade wire and made all connections inside the vehicle. Overkill, I know.
In my case on the right side I have 2 wire only white LEDs and on the left side 3 wires (GND, Reverse, Fog), 6 big white LEDs and 6 small red 3mm LEDs. Used a label maker to label all wires and spade connectors to be able to rewire it if they say anything at the technical inspection.

Printing:
Use PETG, or even better ABS. Infill should be at least 20% fast honeycomb, but rectilinear works as well. I used grey PETG, but the color doesn't matter.

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Prusa

i3 MK3

No

Yes

200

30

I didn't manage to print it out of ABS because of warping.
Should be printed upside down, the part that sticks out of the light should be up.
Maybe it should be longer to mimic the bulbs position better. but it works fine this way as well.