I just bought a truck with an aftermarket under-seat DVD player (MobileVision) and a flip down KEC monitor. I am getting video from the DVD player as well as a weak TV signal on the monitor, but no audio in the speakers. Is it common practice to tie the audio into the factory stereo system, or is it just headphone audio only? I didn't try checking for audio using headphones. I played around with the factory stereo, thinking they tied it into an AUX channel. However, I never found anything that indicated any kind of AUX selection. I don't have any manuals and the previous owner knows nothing about the system. Any help would be greatly appreciated. Thanks.