Anyone know how i can find out which wire is the + and which is the - on a pre out cable from my head unit on factory wireing? Is there a way to test the cable to find out or even a color code for the wireing to find out???

 

The center pin of the rca should be positive. I'm not sure what you mean about wire color but usually each channel has a common ground wire without insulation wrapped around the center conductor that is usually red or white. If you get a fancy cable you can have any color of wire on the inside. Typically if you have the red and white the red is the right channel and the white is the left channel.

 

It's the factory wireing my trying to test. I have 2 cables im testing and it's part of the sub wireing that goes into the factory amp. But i dont know whats the + and whats the - as they are both giving me the same reading because it's AC.