The third light in there comes on when you turn on your park lights. It puts a nice glow out of your headlight. I just replaced mine with Eurolite 194 bulbs. They come in a bunch of colors. I got the blue ones and they put off a hyperwhite color when they are on. Here is a website where you can check them out.

http://www.sounddomain.com/shoplist~...lacement+Bulbs