I have been trying to install lighting in my model rail passenger cars. So far the concept works using LED's, however only in one direction. I know when changing the direction of the current the LED will blow. What component(s) must I install so that when reversing the current the LED will continue to function. Thanks!

 

Two possibilities I see. One way is anti-parallel each LED with another LED. One will light with each polarity. The other is add a bridge rectifier (or 4 diodes)...the car supply from ~ to ~, with the LED and resistor between + to -.

Ken

 

You can use a diode bridge http://en.wikipedia.org/wiki/Diode_bridge. Connect your "unknown" polarity voltage to the AC voltage input Marked with ~. A diode bridge can be built by separate diodes or purchased as a component.