how are you all
i got a 2 farad cap from jaycar
i charged it up using the light bolb
wen the bulb went out i i disconnected it from my battery and installed into my boot buy the time i got to the boot the valtage read out said low so i carried on by installing it.
made my sub sound way better than b4 but the whole reason i put it in was to stop my headlights from dimming to the bass when it hits hard did i do nething wrong in the charging up part.

ahh my spelling

Ditch the cap and think about a better alternator, better grounds, etc.

Chances are, you've done it perfectly.....as the sub sounds better, it may be working.......I did used to work for jaycar, a few years ago, we did have a few problems with them, this is the square gimmick kinda looking one yea?

A capacitor is not a battery, it will not hold a charge too long , its purpose is to smooth out the voltage fluctuations due to the amps instantaneous current draw pushing them cones in and out. It will help with a bit the dimming but to solve the issue you may need a larger alternator or lower volume levels..

thnx guys i just baught a 550 cca battery .
i got all brand new terminals and really good earths so idk aye
just have to put up with it i herd its not too good for ur ecu though

Actually quality capacitors will hold charge for quite a while, some will hold charge for a very long time, the trouble is that most of the capacitors sold for car audio use a cheap high esr caps that are garbage. You need the lowest esr possible otherwise it will do absolutely nothing for you other than empty your wallet.
If this cap is draining itself it must have some parallel resistance draining charge.
I have seen some of these cheap quality caps from name brand manufacturers claiming that you need to actually disconnect the cap from the battery when not in use otherwise it will actually drain your battery, and if you know anything about caps this should be very alarming.....