From the reading I've done, this almost always spurs quite the debate. I have a 5 farad capacitor that I'm trying to decide whether or not to include in my install. The stuff I'm setting up includes:
Stock alternator at 136 amps.
Big 3 upgrade with 0 gauge.
Optima yellowtop D34 at 750 CCA.
4 ch amp at 640 watts RMS (2 ohms x 4): http://www.onlinecarstereo.com/CarAu...cs_ZXi804.aspx
Sub amp at 900 watts RMS (2 ohms x 1): http://www.onlinecarstereo.com/CarAu...BRZ12001D.aspx
This is in addition to about 800 watts of auxiliary lighting installed, however I cannot foresee any situation in which I would be pushing both the lighting and stereo at the same time. That said, I am wiring and fusing the whole system to be capable of running everything at once, and eventually I will be upgrading the alternator to match.
Now if I use the capacitor, this would be for the sub amp only. Probably what I will do is install the whole system without it and then see if I am getting any headlight dimming. But I figured some informed opinions beforehand couldn't hurt either.