Audio Systems: No sound in new stereo, pioneer cd radio, 1991 ford aerostar

Question
I recently installed a new stereo in my 1991 ford aerostar. the old stereo is a stock ford stereo with a equalizer, there is no tape or cd player. I first bought a duraband from walmart and hooked it up with a harness adapter. the stereo would turn on but had no sound. I took it back and got a different unit and installed that one but no sound. I returned that unit and bought a pioneer cd radio and hooked it up and no sound. I checked with the local stereo installer but he said that it is wired correctly and cant understand why it doesn't work. the factory stereo works fine but if i try to install different stereo I get no sound, the radio turns on and all the functions work but I still get no sound. Do you know what may be the problem?

Answer
Yup.
And without seeing, it the best I can do is overview what will fix it.
Run a new short ground wire to the chassis and see if that helps. If not, use a test light and rewire the entire system.
New speakers wires, a fused power wire, a fused memory wire AND a good 'chassis mounted' ground wire.