I have a 99 Ford Explorer w/out premium sound. Head unit is an alpine cda9815 iirc. It was working fine then just quit couple days ago. I unplugged the battery to the reset service engine soon light. Anyways it turns on and all the functions work. I can tune stations, switch source and change eq settings. I get zero sound and it doesn't let any cds get put in. I checked all the wires and voltages and made sure I had good ground and I do. Yesterday I got a new head unit and it does the exact same thing. No sound, no cd intake but all the functions on the display work and is fully lit. Checked all the wiring again still good. I found the factory cd/casette deck put it in and it works correctly. Today I hooked the radio directly to a direct a 12 volt power supply and it doesn't work on it either. Anybody have any ideas?