If you would like to play your phone or ipod (do they still make these) and other audio player and your head unit is old AF, then this is the solution that you're lookin for bub.
Step 1: Uninstall Your Head Unit (It Depends on the Car Make and Manufacturer So Google Is Your Friend Here...
1. Soldering Iron / Gun
2. Solder (Gee... What could this be for?)
4. Audio Jacks (Male or female / It's up to you)
5. Electrical tape
7. Go get 'em attitude
1. Take the Head Unit off the vehicle
Step 2: Soldering the Audio Wire
1. look for the pre-amp pinout... or look for the following labels on the PCB
- R Ch
- L Ch