I'm in the process of doing a truckputer and got the rca cables hooked in my aux inputs (factory installed on the headunit, not one of those adapter cable thingies). On the other end of the rca cables I have a converter that makes it into a 3.5mm plug to plug into the sound card of the computer.

But the problem is I only have sound coming out of my passenger side speakers, nothing coming out of the drivers side.

What can I do to fix this problem?