Re: Interior lights dim slightly when sub hits
First question though... If the interior lights are dimming, that means they're on. So are they on while you're driving or when you are parked with doors open and the engine just idling? If so, then the problem is the alternator is not charging at full current and the battery will discharge much quicker.
If it's happening cruising down the road with the visor light on, the battery is slowly dying. So while you may be running 14+ volts, the system is now causing more draw than the battery can hold.
Gotta disagree with you guys while also agreeing whole-heartedly...
A .5-1 farad cap in this case should fix the dimming (which will NOT fix the problem!).
In most smaller setups, a capacitor will help the system, they are designed to charge quickly & discharge instantly. So while they do add strain to the electrical system, they also ease it when played at low to moderate volume. BUT, when you beat your subs to death, a cap is a cancer to the system. So if that's what you're doing, you need to upgrade the battery first. An OEM type battery provides a lot of cranking power, but only average ampere-hours (steady draw power). If the amp is under 500 watts (12W3v3 needs 300w & warranty is voided at 500w), then a 2nd battery & isolator is overkill. If you still have issues with a better battery, then there is likely a current draw somewhere in the system that needs to be addressed.
I don't bother with a cap on my system b/c it would be useless, when mine's turned up, the lights give up. LOL
You can do it right once or you can do it over...again.