Hey guys, i notice that everytime i press the brake pedal, the interior lights like the speedo, clock, and climate control buttons all dim. I also notice that when i press the button to roll the window up or down, if i hold it after the window has been rolled up or down all the way, the lights dim also. Is this a sign that my alternator is no longer holding a high voltage, and that i should change it soon? What do you guys think?

check the output of the alternator.
it should be between 13 and 15 volts

Check, Clean and Test the Battery, Grounds, and Alt.