01 galant stereo wiring question

[20galant01]

i bought my 2001 galant from a corner lot dealer that didnt have a radio in it. i think the previous owner had an aftermarket stero in it b/c it is heavly modified in the head unit spot in the dash. I tried to put in my Pioneer DEH-P6500 head unit in and it wont turn on. I know it works because i just pulled it out of my Corolla. I bought the correct wiring harness for the galant and everything i need to get it working. It looks like the wires in the dash are all messed up and seperated, spliced, etc... Does anyone have any information as of why my Pioneer wont even turn on, or can i get a wiring map of the stereo in a 2001 galant so i know what im missing. thanks.