speaker work when wired directly but,

I have a 95 Ford Contour in which the stereo system starting fritzing on me. We decided to replace it but having same problem. Hit a bump and the sound went out on it completely and never returned. Looked for loose wires to no avail. We wired the speakers directly to the stereo and worked fine but when  tried to wire through the harness nothing.  Does anyone know if the wiring harness for the speakers connects to something else that could be seperated. Unable to tell as I can not trace it. Your imput would be appreciated.

The problem could be the head unit itself is touching one of the spkr terminals at the back , or one of the spkr wires at one of the spkr's is touching ground(ie..screw, bare metal) .  another way to see for sure is to let the radio play for a bit and touch the back to see if the amp. portion of the radio is hotter than normal

i think in that car there is an internal amp somewheres what you have to do and cheepest way is to just run speaker wire from each device and to the back of radio.