It's the ElectroKen fog light relay mod... I did mine a few years ago and love it... you buy a new relay, modify it per the instructions (again - you should find 'em if you search), and then the fog lights come on with the fog light switch with no exceptions (even when the truck is off... so make sure not to leave 'em on!)
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Warning! Do not sear the top of your neck hole in the molten lactate extract of hoofed mammals.