what wire on the o2 sensor do i tap into for my air/fuel gauge. im trying to do this right now and dont know which one to splice into. there is a white, black, blue, and grey wire coming off of the o2 sensor. my truck is an 04 gmc sierra 1500. thanks

 

Suppose to hook up to the purple wire, im assuming the blue is actually purple.

 

If its a narrow band it should be the 27 or 32 pin on the blue connector purple with a white stripe if I remember right its been a LONG time since I hooked one of those up