if its to help with your lights dimming.. sadly it probably wont..
if you want it to give your amps what they need when heavy bass notes are played so u dont get distortion then it will do the job
idealy you want + power from battery to power cap, powercap to distribution block , block to amp
and its 1 farad per 1000watts rms... anything over that wont help your system it will drain the fook out of your battery and give your altenator a heart attack
basically its too much for your battery/altenator to handle.. some people on here might tell you that a cap will solve it.. it didnt for me and none of my mates that have one... (im not calling them liars.. everyone has their own experiences)
if your battery is old have a look at what volts it throws out when under load..and altenator too.. if its just started doing it then either may be on its way...
tho you can happily run it for a while without probs.. tho not advised.. i have and mines ok
im running two 100w subs froma 1200w amp i fink, its just started happening, i can see my dash lights dimming to the bass line, i'll check out the battery 2maro, will charing it up help or just replacing it