My 3500 did not come with fog lights, I've purchases fog lights and need the pigtails to connect to the truck wiring harness.

 

Purchase an automotive relay (30 amps, I believe) and wire it up to the battery (for power) and to one of the headlight's low beam wires (for activation). I know its a custom wiring job, but that way you get power without going through the stock wiring (slightly brighter, and won't overload the switch in the cab).

If you don't have a kit, go down to Wally world or an auto store and buy a $20-$30 wiring kit that has all the crimps, electrical tape, rolls of wire, etc. in it and use that.

That's my two cents.