Car Stereos: Car Stereo Shuts Off..., sony cdx, ohm load

Question
Hi, i have recently bought new speakers to replace the factory ones in my 1991 mustang gt. i installed four out of the six speakers myself. the other two were installed by my mechanic. when i finish the installing the speakers the sound quality was obviously better but i notice the car stereo would shit off whenthe volume wa turned up at or passed 21. the stereo is not factory and is about 2-3 years old. it is a Sony CDX Gt100. another thing is that when installing the speakers myself i found that i had to cut the wires leading to the old speakers b/c of the factory harness. i tried to match positive and negative wires to the coresponding speaker terminals....could a mixup of wiring be the problem? if so how can i find out which wire to put with the speaker, though i am sure they were connected well.  thank you.

Answer
Auindre, It seems that you may have a resistance issue with your radio.  This can be caused by wiring or components.  As you mentioned, there are  three pairs of speakers in the car, but the radio only has two sets of outputs.  Somewhere, the extra set of speakers is wired into one of the other sets.  Depending on that wiring, the impedance in the circuit could be lower than what the radio is stable to.  If the radio is only stable down to 4 ohms, and the wiring causes a 2 ohm load, it will negatively affect the performance of the stereo similar to what you are explaining.  I would have the wiring checked by a professional, and at about $75, the problem would be fixed.  Hope this helps, Scott