I am putting in fog lights on my 99 silverado that originally didn't have any. Iv'e run wires where they need to go, have a spot picked out for my relay and switch, and even have my harnesses assembled for the lights themselves. My question is though, how do I tap my wiring into the low beams on my pickup so the fog lamps only come on when the low beams are active? I have a 3 pole on/off switch i plan on using but i'm not sure how to connect that to my headlights. I have attached a picture of the diagram i've been using to help clear things up. Also, what is the best way to connect the two lights together? it shows them both connecting to the same wire so i was a bit confused on that as well. Any help is appreciated.

 

The white wire to the switch which is the voltage to the switch connects to the low beam wire. You can find this wire at either one of the headlights. Splice into the wire and run it to the switch. This will make the switch active only when the low beam lights are on. If you leave the switch in the on position, the fog lights will go on and off with the low beams.

 

I agree with oldchevy 's suggestion, you might also be able to pick up the low beam signal from wiring coming from the steering column from the Hi/Lo switch....