Okay, my b16 hatch did this once. I didn't make enough clearance for the alternator when doing the swap, so the pulley was just barely rubbing the frame. This caused the alternator to wear out and not charge the battery. The car wanted to die out if I didn't keep the revs up above 4000 because I had to get the pulley going fast to make a better charge. When I hit the brakes the radio died out, because the power used for the brake lights was taken from the radio since there wasn't much power left. Then I tried to honk the horn and the car died. Had to have a buddy bring a fresh battery to get me back to his house so we could fix the problem. Long story short, check the alternator. Autozone does it for free I think.