whenver i hit my brakes and the my headlights are on, my power reduces dramatically, to about 9 volts, is this normal? i mean my soundsystem can hardly operate when i hit my brakes....is this normal?

 

The headlights and the brakelights are on separate circuits from the engine, so it seems that it's the alternator not being able to supply the load at idle.
With that sound system it's no wonder your alternator is giving up the ghost..
You'll have to upgrade the charging system so it can keep up with the extra demand you are placing on it, at idle.
I guess the Volts are more normal if you hold a foot on the gas too as you brake. 9V is not normal, but you can't trust the dash Voltmeter. Poke a digital meter in the cig. lighter socket (and also at the battery) to get the true figures.

 

see when i first got the car ithought it was the alternator too, but the alternator isnt even a year old now and it still does the same thing...and even if i turn the sound system off, then i still have the same problem with the dimming....im wondering if maybe it could be my ground leads possibly? the battery is brand new too

 

Check your wiring from the Alternator to the Battery.. also take your battery to have it load tested. It may not be holding a full charge.

Also check your grounds for the battery and around the headlights.