1997 Chevy Tahoe rear speaker trouble

Hi i'm new to the forum and i'm hoping someone can help me out here :banghead:. I recently bought a 1997 Tahoe but it came without the stock stereo, so i went out and bought a nice cheap one, and the cable adapter from walmart. I hooked up everything right and turned it on. The problem is that only the front door speakers and the rear cargo speakers work, the rear door speakers do not. I opened up the rear door panels to take out the speakers which is why i thought they were not working, so i took them out and put in some speakers i had bought a while back ago. They were still not working, this was strange to me because i know those speakers are good. So i'm not sure what the problem is here, if anyone can help me please, thanks in advance

those wiring harness things can be rather generic, you need to find the actual wiring diagram for the vehicle

Probably the wal mart wire harness you bought. check a shop manual for the wire diagram like paul stated and make sure your rear speaker outputs from the head unit match to the harness, and from the harness to the chassis harness.