Help wth my stereo
 

I had bought a GPS stereo from ebay and believe its oem and worked for 5 mos now but whenturned it on yesterday all works fine but no sound at all from the steering wheel are the unit.Checked fuses cause I had seen one for the radio and one for a AMP it says.Do ya think the AMP is out ae what,and how can I check this to conferm.The part number for the unit is 15204335 and is that OEM were i could take it in shop and say it was there when I had bought it.The H2 is a 2003 but bought a 5yr exstended waruanty.Please help with any thing yo have.And you think I could put my old unit back in and if it wrks then its not the AMP, areis there a sepeate AMP, is this how its hooked up are what??Thank you for any one help an Hummerbuddy and have a great day.