i need a cap

Personally, I would recommend putting a sealed lead acid battery near your amp. Wire it just like you would a cap. A battery will push more current than a Cap will all day. No matter what you do without upgrading your alternator is going to put strain on your charging system.

True but forget to fuse next to the battery1993 sdv

Alpine 4x6 6x9 5 1/4 swr-10d4

alpine v60

12.5 VGA flip down

Nettop pc w/10" touch screen

78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

Nahh... Who needs fuses? They just keep your car from catching on fire :P

That's kinda the point ..... fuse within 15" of the battery1993 sdv

Alpine 4x6 6x9 5 1/4 swr-10d4

alpine v60

12.5 VGA flip down

Nettop pc w/10" touch screen

78nova

5-re audio 5x7 ,10" sub &

Xtx-500.5

"Take the faceplate off get the jumperpack"

And don't forget to isolate the battery when not being used.... And it's TWO fuses if it's a 2nd battery - ie, one from EACH battery. But this is a dead thread. The OP's lamp dipping problem was solved with a cap. Granted, it is not known if it would have been solved with better wiring (the Big-3 etc) or by using smaller & cheaper battery in lieu of the cap, but in this instance, a cap solved the problem and it has advantages over a battery (ie - maintenance & isolation is not as important). This was not a case of filtering for amps - it was merely for the filtering of headlight power.