I did my install on an 04 nissan 350Z roadster, basic stereo package (non-bose). I used the METRA 70-7550 wiring harness and double and triple checked wiring. The wiring is good but I am only getting sound on the left rear speaker. Any ideas? I don't want to think that it's a bad HU but I'm starting to think that the HU is shot?!?!