I have a JL 12 W7 and a JL 1000/1 AMP WANTED TOO GET A BATCAP JUST DON'T KNOW WHICH SIZE I NEED

 

You can use one x400 model. Enough for 1000w.

 

batcap 800 should be sufficient, i used 2 batcap 800's on my memphis mojo 2000d and never had any headlight dimming, but once i did have a memphis hc100 (800wrms) and ran just one batcap 800 on it with stock alternator and it worked fine as well. they are 190 new at a retailer but sometimes you can go to usaci forums and get them for about 100 shipped used.

 

crazy, I live maybe 5 minutes away from where they make these. I ride by there 4 or 5 times a week. I wonder if I can just go by there and buy one.

 

Have you replaced to a ho alternator?
First thing you should do is grounds and alternator. All a batcap will do is store energy not MAKE energy the alternator does that.