A single 4-Ohm coil subwoofer is driven at 4-Ohms at all times. Or did you cut and splice RCA cables into the stock speaker wire? There is only front and rear speaker input but the amp also supplies a woofer? This is a good idea if you ever plan on changing the stereo as your RCAs will already be ran. You could add additional subs to your system using these outputs.
Everything works fine but sometimes i get a loud humming sound from the subwoofer.
Adding RCAs to a Standard Car Head Unit
Adding a subwoofer and amplifier to your existing stereo is a great way to improve the bottom-end output of your system and is one of the most common upgrades performed on a car's audio gear. If I connect and amp for a subwoofer to the stock sub speaker wires. Its got 2 RCA out-put side i dont know which one to use and about 16 diffrent places to put the wires into i thought i only needed 4 slots. Step 2 Position your amp and speaker in your car. I had my installation done by so-called professionals.