It is dead easy. And LEDs make directional lighting all of their own accord.
An LED passes current in one direction only. So if the lamp does not light one way, switch the wires and it will light up.
YOU NEED A RESISTOR in series with your LEDs. You must limit the current rather than the voltage.
If you put one at each end of the locomotive, attend to how they light with respect to which way the engine is moving. They now make some really, really small LEDs but I have not used them yet.
On the consist below, I kept the light conducting plastic between the head lamps and the place where the lamp is installed which is near the roof of the unit. I used one RED LED where the white lamp used to be and two white LEDs along side of it. The white lights come on when the equipment moves forward, the red lights come on when the car is on the rear of the train.
ROAR
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Is it possible to install LEDs on a dc locomotive? Is it hard to wire?