ScottC400

i know this problem has come up many times and i have searched and read but still cant figure out my problem. i am trying to rewire my stereo to run without an amp. i used the four positive speaker wires from the amp input harness to splice them into the amp output harness. so that they would be powered directly from the stock head unit. now for the negative speaker wires i connected them to the signal ground. when i tried this i got one speaker to work but the sound was very low, but when i connected all the negative speaker wires to the signal ground i got no sound from any of the speakers. i was wondering if anyone knew what the problem could be. my stock amp is blown.

i tried to wire it to an aftermarket amp but i was wondering can i use the 12v wire that ran to the stock amp to power the aftermarket amp. when i tried it, it would not power it. so if anyone could help i would greatly appreciate it.