Anyone have an idea why when I get on the brake pedal my rear speakers cut out and the headunit dims for a quick flash. Do I have some bad grounds? It doesnt cut out at any other times, not when you turn the headlights on, nothing. Just the brakes.

 

It does sound like a power problem (bad ground/voltage drain). The first thing I would do would be run a new ground wire for the head to a piece of metal (ie the firewall, etc). If you're feeling adventurous since you're already back there, you can also run a new 12v line straight from the battery. Those two things will probably take care of your problem.