I was fiddling around with adding an extra speaker to my car system and think some wires got crossed, causing all sound to quit. I put everything back as it was before, but still no sound. I took out the unit and checked the wire connections, which are all good from the unit to each speaker (by testing with a portable radio). I reset the unit, and still no sound coming from the unit to the speaker wires. External 15 amp fuse is good, and radio/CD display face seems to work fine. What else can I try?