I recently bought a Pioneer stereo system (FH-X700BT) for my 2008 Hyundai Sonata. The Sonata still has its factory speakers. The factory stereo was working fine, I just wanted something other than a CD player (aux, bt). After I connected the stereo wiring to the wiring harness and plugged it in, the music couldn't even be heard over the AC, whether from the CD or radio. I plugged the old stereo back in to be sure it was the new stereo causing the problem, and the sound was loud as expected. I am almost positive that none of my wire connections are bad, and pretty sure they are all matched up properly.
What should be my next step in troubleshooting? What are some things that could cause this, and things that I should be wary of? Should this be working normally or is there some sort of compatibility issue I overlooked?