Not a diagram, but hope this helps. I got these from somewhere. If I remember right they are from a 64 GMC so YMMV

http://dl.dropbox.com/u/907387/GMC%20project%20folder/fuse%20panel.jpg

http://dl.dropbox.com/u/907387/GMC%20project%20folder/fuse%20panel%202.jpg


1963 GMC 1000 Wideside