Battery only draining when my car is running

I had bought a 2000 cavalier z24 2.4L the stereo was not in
it and had the factory harness for the radio cut, I drove it
around like that (capped wires) for a couple weeks. I had
someone try and hook up a stereo and couldn't figure it
out.somewhere along the lines I had to take the stereo out
and cap the wires again because it are up my battery. I
replaced the battery, alternator, and the fusable line. Had
the battery and alt. Checked and they were both good, I
have tried everything. Someone had told me that I might
need to get the exact same stereo wiring harness that is for
that year make and model. Re solder the wires back to the
rightful area. Any help on this issue please would be greatly
appreiated