Evans has a wide variety of LED lights that work on AC or DC from 7-19 volts. Just hook up the wires to the ground and center rail pickup and they work well. They also have blinking Red lights that look good. There are circuits you can buy that will maintain a constant voltage as well to reduce the flicker but if you are rollers are clean and the springs are tight enough the lights should stay on most of the time.
If you are trying to light the side markers on a caboose I find a wider bulb works well they need to be aimed at the inside lens to light up the colored glass found on some cabooses. The LED bulbs do not work as well as grain of wheat incandescent bulbs if inserted in a tiny hole for the side lights if there are different colored lens side and rear on the lamp holders. As the LED lights tend to be brightest when viewed directly. You can file down the LED lens a bit to get the light to spread a bit or insert a glass or plastic tube through the hole where the old grain of wheat bulb fit, then shine the LED directly into the end of the glass/plastic tube and it will help distribute the light a bit better.
