no.

a cap WILL NOT help

all it does is puts more strain on teh electrical system

think about it. your poor little stock battery has to now run teh amplifiers AND recharge the cap. its just gonna make the prob worse

first thing to do, get a big battery. recomend an optima yellow top, or just about anything odyssey

then, upgrade your vehicles grounding. run a nice big fat length of 0guage cable from teh battery negative to the chassis

that will help the dimming

im not pulling this out of my arse, this is coming from real world experience. i had over 3kw rms in my last stereo that i competed in sound quality comps with, that i spent around 8k on

im not a noob when it comes to car audio