Originally Posted by b00gers

A cap is NOT a power source for the amp. You want the powerered subwoofer wired directly to the battery with a fuse close to the battery. I dont know know how thick the wire is to your main relay. If the lights dim, that just means that the subwoofer is drawing more power than your alternator / battery can supply at the moment. When the light is on, and you are at idle...your alternator is producing the least power. So the power used to power the lights is diverted to the subwoofer for that small moment causing it to dim.

But if you are only experiencing this at near max levels...which you are rarely at, I wouldnt worry too much.