I am going to put fog lights on my truck and was wondering if it was a factory option, would there be wiring arlready there in the harness?

I went to my supplier's warehouse to day and and yes they had them. The 9104 blubs with no R, 100/80 watt, for $5 each so I picked up 2 more.

Will the 9104s slide right in or are there tweaks to be done?

They look just like the 9004 blubs that are in it now. They slide right into the holder, twist the retaining ring on, and plug it in, there's no mods to do.