people usually hook up their capacitors in between the wiring of the battery and amplifier.. sorta looks like this..
BATTERY========CAP======AMP
the thing is with a cap, make sure you have the polarity right when you hookin that bitch up. if it goes the wrong way, that fucker can explode and fuck you, and your shit up. the chemicals inside the cap react to something and gas builds up, blah blah. but yeah..
you hook up the positive of the cap to the positive to your battery. and also hook up another wire from the positive of the cap to the positive to the amplifier.
then have SEPARATE negative wires for the cap and amp... but make sure the wires from the cap to the amp are as short as you can get it, the power signal will be stronger that way.
but yeah, if you usin a cap on just your tweeters, you wastin money cuz tweets dont take up that much power from your battery. ESPECIALLY if you aint got an amp hooked up to it.