I use a RCA cable to hook up my iphone to my stereo in the car. First cable I used was a cheap RCA, the very first I found. That was a bad idea. The heat from the sun totally screwed up the cable, to the point where I could only hear music coming from one side of the car and also a lot of hissing. I bought a thicker, better quality RCA and it's worked great ever since.
Don't underestimate the heat inside a car. I would avoid leaving any kind of electronics in it on a sunny day.