Attached is a PDF describing a way to convert LionChief passenger cars from incandescent lighting to LED lighting. (In this example, Santa Fe streamline passenger cars.) It reduces current draw from about 154 mA down to about 12 mA. Also, you won't have to change burned out incandescent bulbs anymore.
Lionel has produced the cars with both incandescent and LED lighting. Lionel's LED lighting approach has a small circuit board at each end that includes a keep alive capacitance. Each truck independently powers a board, so the boards are in parallel and their total current draw is about 36 mA. Pretty good, but not as low as this conversion.
While the conversion does not have a "keep alive" capacitance, it does wire the trucks in parallel so all wheels and rollers are used to power all of the LEDs. This should go a long way to prevent flickering from dirty track.
The conversion is a bit physically crude, but it is simple and works.