Success! With the live wire connected to a power source, and the body grounded, the LED fires perfectly. Once again, you're going to want a resister ...
Now we need a way to keep the LED from shaking all over the place inside the signal body. All I had on hand was some cardboard, but i'm going to go back and use some heavy duty rubber, and glue it all in. I just needed something temporary. For now, you get the picture.
Whatever you choose though, it needs to fit snug inside the space the bulb use to take up.