Car Stereos: audio system in my 1990 Mazda Protege, mazda protege, power source

Question
I have a question about the factory-installed audio system in my 1990 Mazda Protege LX 4 door sedan. The audio system does not power on. I checked the fuse and it's fine. I bought a meter to measure electricity and tested the radio and the power source. I found out that the radio wasn't receiving enough power to turn on. I need help. What do I do to fix that?  

Answer
Hi Bic, thanks for your question.
You mentioned you bought a meter and measured the voltage at the radio AND the power source. Can you tell me firstly where exactly you measured the voltage (at the radio? What color wire did you measure on the harness and where were you grounded with your meter?) and lastly tell me what voltage reading your meter gave you? This may better equip me to help you troubleshoot this.
Thanks, Rob