I've been trying several ways to install lighting into passenger cars. So far, my favorite is the ESU strip, with its decoder and fancy options. There are two others I have to test: Roco and Model SF Production - especially for the Corail since the lights came from under the rack.
I know ESU and Roco won't really give that effect, so I'll have to see with Model SF. For now, let's take a look at Roco.
Roco 40420
First step is to open the car and separate the various components to access the bogies - it is well explained on the instructions:
The pack consists on the 2 power pick-ups, the main strip, double-side tape, and the interesting part: the LEDs can be positioned as needed and the electrical connection is done with tiny clamps or couplings. Pretty smart!
Now, we can run a test before closing everything back:
I wasn't quite clear if the strip would work even without a decoder, since there's a plug for it but none is provided with the kit. This is a big difference from the ESU one. For Roco, a tiny decoder can be installed for the fancy options. However, even without the decoder, the lighting works well in DC and DCC.