flicker of lights

every time i push the brakes or have the radio loud the head unit and the dome light flicker.btw!i changed the battery and alternator already!

Do you have a sub in the car? I would hook up a volt meter to the battery while the car is running and see how much voltage you are getting. Then push the brakes or turn the radio up loud to make the lights flicker and see if the voltage drops a lot.

I think your stepping on a wire. Not physically, but the pedal sliding back and forth under the dash.