Thanks guys. I will have to look at which is easier, I think going into the fuse box might be easier and more room to mount the horns on that side. Like I said, I should have looked before I leapt since my F250 is brand new (bought it last month) I didn't worry about modifying my 96 F150 that I sold to buy the 250. Pistol Pete, I bought the twin horns on this link. But my new truck doesn't have as much room as I had thought for mounting them.
http://www.wolo-mfg.com/elec.htm