Stereo HEADACHE, no sound from rear speakers (NOT BLOWN)
 

When I bought this truck the radio was completely dead, not even the clock worked. I checked the fuses and they were fine and had power, so I tossed it and put some old cheapo aftermarket one in that I had pulled from a car I had a while back, which worked, but no rear speakers. I thought maybe it was a problem with the headunit itself, and it had other issues, half the buttons didn't work, had crappy reception, etc. So today I got a brand new HU, wired it in, still no rear speakers, it actually came with 2 6.5's, so I pulled the door panels off and replaced the speakers, and STILL no sound. My dash speakers work just fine, and this is far from my first radio install, but I'm a little bit baffled as to what could cause this, I triple-checked that I wired things correctly. I've tried to find some info, but it seems almost everybody else with this problem, which is apparently quite common...replaced the speakers and they had sound again.