forsaken6661

so i just bought a 2004 pontiac montana. the stock radio i believe has a blown led and the previous instrument panel had been replaced causing the theft system to lock it so there was no way to get it unlocked. i now have a aftermarket radio from my old car but i cant seem to get it to work. i got this wiring harness GM Radio Harness - Power and 4-Speaker plugs into the factory radio - Radio Wire Harness 71-2003-1 METRA which everywhere i look says is the one i need but it will not give my radio power. am i doing something wrong or could it be because of the anti theft system? any help would be greatly appreciated i really dont want to take this somewhere and pay to get it done.