If you're in foggy weather and turn the fogs, the beam is directed to the ground just under the fog, lighting the foreground and increasing visibility; if you were to turn your high beams, the beam will hit the fog and reflect back in your eyes blinding you and decreasing visibility. That is the reason why they are set to not run at the same time.
I know you asked how to wire them, but this may help if your looking to run fogs and highs for short periods of time, just how I do it if running late in the trail. I'm going to give you my 2 cents.....well, actually my 1 cent.
For the TJ guys, you can bend a leg on the fog relay to allow them to run with the highs. This does not work on our grands (WJ), I already tried. What I do:
All it takes its a penny, If you have your lows and fogs on, and you flash your highs, you will notice if you hold the lever before it "clicks", the high beam will come on and the fogs are still lit; if you place a penny at the base of the lever, it will hold it in that spot allowing you to have all three on at the same time; now it's that el cheapo mod or what?
As I said, I do this ONLY while offroad, do this at your own risk, do not place other drivers in danger by shining all this light on the freeway.