Ok, ill take a stab on a couple of issues.

The ballasts of the HIDs are designed to NOT fluctuate voltage the bulb, because it would damage it. I dont know how, I just know it does.

Second, lights in your car are meant to run at 12v. So when the voltage dips under 12V, they are starved....and basically, like a dimmer in your house, the lights get dimmer. Im sure that Macgyver and phil can explain this a lot better than I can.

 

HIDs, like fluorescent lights, require a voltage spike to start them up, then the running voltage can be significantly reduced...that's the job of the ballast, to provide all of that. Changes in input voltage will not change the output brightness, except to say the bulbs will extinquish once the available voltage drops below the operating voltage point.

Incandescent bulbs, such as the interior stuff, will change with varying voltage levels, including getting brighter with 14V. The bulb is a resistive element which glows when current is passed through it...increase the current and the bulb changes brightness. Increased current also increases the resistance, thereby reducing current, so in some ways they are self-regulating (to a point).

Our map lights are set up in a neat kind of way, allowing the doors to turn on both lights, but the switches to only turn on one. This is done through a couple of diodes which drop the voltage about 1V. Next time you get in the car, open the door and look at the brightness of the light. Now hit one of the switches and note how the light on that side increases in brightness slightly. By using the switch, you have essentially removed the diode (and 1V drop) from the circuit.

 

I just installed a capacitor in a car. First time installing one, it said to charge it up before installing it. The process to charge it takes a few seconds. When I talked to my friend, he told me there's not point in charging it since I'm running it parallel with my system. So do I charge it up before installing it or just pop it in?

 

If you're not running it in parallel with your system, what are you doing with it?

 

It is again, my "expert" opinion there is no other way way to use a capacitor.

 

Well, he could try to put it in series, but he won't be listening to music for more than a few seconds.

 

Well the guy was simply saying that, and that it doesn't need to be charged prior to installing it. So is he right or should I charge it first before I install it?

 

Well, if he suggested using it in series, MY suggestion is don't ever listen to this guy again. I'm not sure if the caps come with a higher value resistor for initial charging or not, but if it does, I suggest charging before installation...why shock your battery more than it has to be?

 

The capacitors that some of us install in our systems is best looked at as a quick filling (and quick emptying) surge volume if you will for the current that our amps require during large load changes. When a big bass hit comes it increases the load on the entire 12V system which can either be fed from the battery/alternator or from the battery/alternator and the cap which provides the initial inrush or outrush. The cap discharges much faster into the load than the alternator/battery alone and charges back to system voltage ~14.4 volts much faster than the battery without cap previously "drained" by large load change, thus smoothing out the entire system voltage levels, i.e. not so many mountains and valleys and with sufficient capacitance will stop dimming of incandescent 12VDC bulbs. I hope I made that clear enough. It is hard to try to explain for me, but it is easiest to think of it as a surge volume to smooth the voltage fluctuations due to large load changes. Yellow top batteries are successful in limiting dimming because of their deeper cycle that will allow for the deeper discharge during load changes without as dramaticaly effecting system voltage.

As far as precharging the cap prior to install, this is to prevent welding the wire and terminal when you try to connect the wires to the cap between +12V and chassis ground (an uncharged cap appears as a dead short as was mentioned earlier) and it would make a big spark and probably damage your terminal and/or wire.
This is my take on how stuff works....correct me if I am wrong. HTH