I am trying to replace my factory stereo with an aftermarket stereo. I have had the power entenna and the wiring harness hooked up. I don't have any sound coming from the speakers. I can hook the stereo directly to a speaker (off of a boat) and sound is fine. Hook back up to speakers in vehicle... nothing! Any ideas of what may be missing?? I have tried with two different stereos but have the same results. Any suggestions??