Originally Posted by J.A.

In order for the fog lamps to light up, the fog relay needs to be energized. To become energized it needs both positive and negative available at the coil. Part one brings 12V+ positive to one side of the coil anytime the ignition is on. Since negative is at the other side of the coil anytime the headlight dimmer stalk is in the low beam position the fogs work "anytime" as long as you dont choose the high beams. As soon as you switch on the high beams or the "flash to pass" mode, then negative is removed from the coil and hence the need for part 2. Part 2 brings ground (negative) to the respective side of the fog lamp relay coil whenever the fog switch is on regardless of the headlamp dimmer position.