Instrument voltage regulator

Hmmmm, I have a new external regulator and my dash is out. My fuel gauge still has the internal stock setup because I don't know how to make the changeover correctly. (the absolute best way) I for one would appreciate a link or a post describing the foolproof way to use the new external regulator I already own so I can make the change before I reinstall my completely assembled dash.
DR:coffee2: