Quick question about aux cable DIY
The purpose of the series capacitor in an audio circuit is to remove DC bias from the signal. The larger the capacitor, the lower the frequency that can be passed from one stage to the next. Using a larger capacitor is not usually a problem unless there is a specific need to filter low frequencies.

Normally electrolytic capacitors are polarized and the negative lead must be connected to the lower voltage, but Visaton's Tonfrequenz-Elko electrolytics are bipolar and can technically be oriented either way.

For best performance though, you'll want the lead connected to the can to be towards the lower-impedance stage so that absorbed RF has a lower impedance path to AC ground. So the lead that connects to the can goes to the car, and the other goes to the audio device output.