2003 Monte Carlo woes...need help asap!

Need help ASAP! Replacing sisters factory CD player with Pioneer 5500. She used to have 2001 Malibu, when 5500 was installed it required the "t" harness to relocate factory radio to trunk. I was hoping I could use it in this install, possibly plug and play. Just like the Malibu, the door chime is played through the speakers. Problem: There are 2 harnesses on this radio. One is the same as the Malibu plug, the other is smaller. I can play the factory radio without the smaller one plugged in. I unhooked the factory radio and plugged it into the end of the T harness just like the Malibu. The Pioneer plug is already wired from last time, so I plugged it into the back of the Pioneer. I ran the red wire into the fusebox like it was in the Malibu. The Pioneer turns on but no sound(antenna hooked up, tried playing CD as well). The factory powers up like it did in the Malibu. I forgot to add there is what looks like an amplifier attached to the rear deck in the trunk. HELP! Am I forgetting a harness, or is the T even needed? I have been promising to install this for weeks, I'd like to finish it today. Thanks in advance...