I could make a bunch of guesses. Reality is.. GM color coded things and that's an evap color.

Do you have a ps pressure sensor on the bottom of the pump or something like that? Here's how I'd try to find it. Move that wire around in a circle as far as it'll go. Then subtract 2-4 inches of distance because every wire has slack, except your alt connection (it's a 3100 thing). From there.. search for anything that is missing it's connector. Also hook up an OBD reader and see if any codes/sensors aren't reporting or have reported an issue.