Rich, I added BOTH to my 01 ST. They use the original light switch. The switch stays all the way to the left position and I leave the fog light switch pushed in. During the day the headlights come on, just not as bright as night time. The fog lights stay off. When it gets dark enough the go up to full power and the fog lights also come on. I bought mine new and had this put on at the dealership when it became available as an add on. You had two different kits you could get. One was just the daytime running lights. The other kit had the daytime running lights and the automatic headlights. The later one was the one I got.