Since this topic comes up all the time, I thought it might be nice to revisit it briefly. Here's the RailKing Reading Crusader Observation Car that I upgraded to LED lighting and also added passengers. One of the issues of the observation car is getting decent lighting to the marker lamps and the rear tail lamp.
For the shell, I remove the socket and wiring for the rear bulb, and I slightly extended the wiring for the front bulb and added a connector. I added the matching connector onto my LED Lighting Regulator Module to make it easy to separate the roof from the car and not have it dangling on a wire. I added a sprinkling of passengers, including a few standing to add some additional interest.
Here's a quick shot of the finished product.
Here's the interior of the car before final assembly. You can see the pigtail from the old light socket with the connector attached.
This is the front detail of the roof interior, In the roof section, I stick the lighting module to the ceiling with double-sided foam tape, it's well above the sight line from the windows. I run the wires over to the LED strip that runs down the center of the car. You'll also notice I bend the tab on the regulator down so it doesn't show in the window.
Here's the rear detail of the observation car roof. This is how the markers and taillight are illuminated. I take two LED's and form the leads to suspend the LED at the correct position. They're glued to the roof once the associated wiring is connected. The taillight LED is simply glued directly to the taillight lens in the roof. Nice thing about CA adhesive, it dries clear. You can see the 470 ohm resistor in series with the three LED bulbs, that resistor is selected to provide the desired level of illumination of the lights. Since each segment of the LED strip has a 150 ohm series resistor and three LED's, these will consume about 1/2 the power of one of the three-LED segments. The color temperature of the three marker/taillight bulbs is selected to be the same as the LED strip, so any incident light from them just helps illuminate the rear of the car interior.
In total this car has 18 LED's, and it consumes a total of 25ma of track power. The side markers and taillight are now nicely lit as opposed to "just being there" as they were with the factory lighting.