there was one thread about cap stuffs that you must read. some ppl distributed some very honest opinions. i think the first thing u need to do before buying either a cap, an alternator, or a battery is to check out ur current battery and alternator at a shop. maybe ur alternator is dying and in that case, a cap won't help but makes the whole thing worse. why, cuz u are drawing more power from the alternator. a cap acts like an absorber/releaser to stablize the current to ur sub(s). if the cap feels that ur amp and sub(s) are drawing too much power for the alternator to catch up, it will release power and vise versa. so adding a cap is not the best solution to cure light dim. you difinitely have to test ur alternator first. maybe 180amps or more is all u need