2005 LE with JBL Stereo adding subwoofer
 

I'm trying to put an amplifier and a 12" sub in my car while using the stock stereo. I hooked it up today, and it's nothing like it should be. As you turn it up, the bass kinda fades out. I did tie in on the output side of the factory amplifier. The reason for that is there are no - wires coming out of the factory stereo. Has anyone else ran into this and have a solution??

you need to tap on to the factory harness before the factory amp and install this rca kit PAC SNI-35 Adjustable 2-Channel Line Out Converter and this will allow you to connect the aftermarket amp inputs the right way .