As mentioned in the previous post, I worked on this 2.5 years ago and was not happy with the outcome. I used cheap led strips, but the main issue was that all strips were controlled and wired to one decoder. That decoder has obviously a limit on the current the lights can draw and it could not handle all the LEDs for the 3 units. Since then I use the ESU lighting strips and I plan on removing what I've done to fit those ESU strips.
I'm posting here pictures from my work at the time:
I remember that there are two colors for the light and that I was using some Miniatronics connectors between the car. I have to revisit that!