Besides the speed sensor wires, there is one group of wires going to the big plug on the top back of the transmission. All of which are small gauge wires, all the same. The wires you speak of go to the transmission range sensor on the 03 and older Grand Prix's, and they don’t use that in the 04 newer cars. Hence the need for a diagram. I still might grab that purple wire from the starter and follow it, it’s a bigger gauge wire for sure than any wire going to the trans.