I just recently installed a aftermarket radio in my 99 gt and used the long grey adapter and the square box with 8 prongs inside. The headunit powers up but no sound. Nothing.. Theres another plug but its square with 6 prongs? This has never happened to me before can someone please help?

 

Got the speakers working but now theres no power to the head unit???? Wthh

 

make sure you hooked the blue amplifier turn on wire to the blue/white or blue remote turn on to the radio.

IF it is not powering up start by checking fuses. I just start in one corner and work my way across until they are all checked. Takes 2 mins and will make sure it is not a fuse.