Is a cap worth it ?

ok, all of you guys that say caps don't help, answer me this:

I have a 240 amp alternator, 2 Optima Yellow top batteries, 2ga. wiring to my 1000watt amp that is pushing 412"s, and my headlights still dim.

This is in an old (1979) bronco with not very many electronics to speak of that would also be draing power. Noone thinks a cap would help???

Take a voltage reading at your amplifier. Does your bass start out clean and crisp and then turn to mush? Do your headlights only dim at the beginning of a bass note and then go back to normal level, or do they dim for the entire bass note? To test this park your bronco in front of a wall or garage door at night and play a song that has long bass notes. Then look at your headlights and see if they dim through the whole bass note or just at the beginning. If just at the beginning then a cap might help you a little.

A capacitor can certainly help in the ways it was intended: to help compensate for the short duration dips in voltage caused by high current draw.  This is called a ripple filter, and is what caps do best.  But no capacitor can help if your alternator cannot supply the current demand.  The voltage dip during long musical passages is often too severe and lasts too long for the short discharge duration of even the largest caps to have much effect, and then your discharged capacitor will place additional load on the alternator and electrical system as it attempts to charge back up.  The alternator is the primary source of power in a running vehicle with a properly operating voltage regulator.  A cap is a band-aid for a short-duration transient voltage issue and is intended to help the amplifier sustain its output, it is never a solution for an overloaded electrical system and it will generally have very little effect on dimming lights.

Greenbroncoguy, your system has a problem.  Something is not operating properly or is not setup properly, or you are simply not getting the output required from your alt.  As customsuburb asked, what is the voltage at your amplifier?  I suspect your engine is not turning fast enough for the alternator to produce the current required.  Or you have a bad belt or something.   Remember that an alternators max output (in your case 240 amps) is the rating ONLY when it is being turned at its optimum RPM by your engine.

I haven't checked the voltage at my amp yet, I will tomorrow as it is storming now (typical Florida weather).

As to my alternator, after I bought it new, I had it checked and the dude printed the specs out and were as follows: 248 amps @ 5000 rpm : 167 amps @ 3500 rpm : 101 amps @ 2500 & about 90 amps @ about 800 rpm. I say about because I have a bigblock engine with a very large cam and it idles erratically. However, my lights dim when I am driving down the road also, not only at idle when it is much worse. Since I have a bigblock and will hardly ever turn it above 6500, they put a smaller pulley on the alternator to make it charge more at a lower rpm. So, I dont think my alternator is the problem.  Also, my belts are new and I keep them tight so I can probably rule that out also.

have you upgraded your grounds?... next  is the wire from your alt. to your batt. 2 awg? 3rd how long is the 2 awg run from alt. to your last batt.?

you need to have 2 awg grounds from your alt. to your frame. 2 awg from your batt's. to your body at least and 2 awg from the body to the frame..

My wire sizes are:            

               both grounds from both batteries to the frame are 0/1 ga.:  the wire from my alt. to both batteries is 2ga. , the short one is about 2 feet long, and the long one is about 5 feet: I don't have any grounds that go directly from my battery terminals to my body, but I have alot of ground straps throughout my truck that go from my body to my frame, I added like maybe 10, and there were already maybe 10 more.