install jensen HU in '91 protege

Hey folks I'm trying to install a jensen cd3010x HU in a '91 mazda protege.  the unit powers on and behaves correctly except there is no sound. not a peep or a pop.  i know the speakers are wired right because i can plug the factory unit in and everything is peachy.  i've connected the harnesses and checked them against the diagrams for the car, the HU and the harness pkg.  the only wire that is comes from the car that doesn't connect to something on the HU is the dimmer wire. I call it the dimmer wire because that's what it's called on the harness diagram.  the car diagram doesn't show a wire in that spot but it is there.  i really don't know what a dimmer wire is.  should i hook it up to something? is that even the problem?

any help would be gratly appreciated.  thx.

Have you tested for factory amps? Have you tested your speakers for impedance? Most factory radios will play a dead speaker, but most aftermarket radios do not as the protection circuit kicks in. Try this, get in your car and shut the windows and doors and turn the car to accessory. Then while being quiet, turn the radio on. Some radios will actually make a popping noise to the speaker that is shorting out. Long shot, but I would do that first before tearing the radio back out.