here's a link to the electrical FAQ section. It's covered in there.
http://67-72chevytrucks.com/vboard/s...d.php?t=345919
DO NOT try to just plug it in, and be VERY happy you didn't. I did years ago, and the end result sucked big time. My buddy was there and was laying in the dirt laughing when he saw the fuel guage sping a couple laps around before crapping out in a puff of smoke.