Quick background:
2007 Mustang GT
Kicker 750.1 and 12" L7
Aftermarket 200A alternator (~130A stock)

I expected the upgraded alt to keep up more but the lights dim just as much if not more than before (I also took a toll on my battery driving with just it when my alternator died, that may be why?)

What would be the next step for the power system? The performance of my car is a factor too so adding a lot more weight or load on the engine isnt the best option. Should I just add a cap? If so how many farads?

did you do the big 3 upgrade with new alternator?

whats your amp ground like? did you sand off the paint and stuff?

is this only headlights dimming or all lights?

are you sure the subwoofer is hooked up the amp in the correct configuration?

caps are garbage, do a big 3

this. if you do a big 3 upgrade and your lights still dim, check out tenneyalts.com i think it is. for a new higher output alternator.

Im thinking he hasnt done the Big 3 yet.. with a 200amp alt he should be fine.

Id say Big 3 and a good battery.

Do you also have an amp for the components?