I'm wiring up a Sony cd player in my 77 MGB. I have power and everything works properly, except there is no sound coming out of the speakers. the HU is powering up with the key, the cd spins, the memory is staying without the key etc. i have new wire run to the front and rear speakers, new rockford speakers up front, and older pioneers in the rear. I'm not running an amp or anything. I'm only using 3 wires (red, yellow & black) other than the speaker wires. what could be the problem? Guru's ... please shed some insight.