1996 Chevy Astro Need wire diagram for a fuel pump

I have gotten a 1996 Chevy Astro Van with no fuel pump in it. When I went too the parts store to get the correct fuel pump I ask the Tech there which wires are positive, negative, and so on. He was clueless. So I don't wish too hook it up wrong because I am afraid something bad will happen. They're are four wires: Two big thick wires are black and gray; the two small thin wires are purple and black with a white strip. I wish I had a diagram or something to describe the hookup of this. I can't find no picture diagram or description on the net.