Does anybody have a '78 stereo wiring diagram cause I can't seem to figure out what any of the old wires are.

 

Don't worry about what they are. Go to Best Buy and get the adapter plug for the new stereo to adapt it to the old plug. Then you just plug the adapter into the wiring harness, and wire it to the new stereo. That also avoids chopping the old plug off and hacking up the wiring.
The adapter plugs are around $20.