Here is a kit I put together for adding interior lighting to passenger coaches, cabooses, etc. The special thing about this kit is that it functions in both directions on DC, and even works perfectly on DCC. As long as there is 4-18 volts on the track, the LEDs will light. Also, it offers a "constant-intensity" ability that will keep flicker to a minimum as the coach rolls down the line. Soldering skills and equipment required.