I have a train layout, with lots of controled blocks. I want to connect a light to each block. I have resistor connected to one leg of an LED. So the resistor end and the other led end are connected to the track. But with the power on, I want to keep the led light in either direction. The light only stays on in one direction. The led light shuts off in the other direction. How can I keep the led light on in either direction. HELP!!!!