if its shorting to ground, it would be blowing the fuse, and the current would not even be getting to the bulbs. alt. output should be 13.8-14.2 volts, so definatley make sure it isnt much over that, and that it stays at a steady voltage. Also make sure there isnt anything else wired into that circuit that could pull excessive current through the bulbs, that the contacts are clean and making a good connection with the bulbs, and that water and mud are not splashing onto the bulbs somehow. You should also make sure it has the correct size fuse in it.
the brake switch is mounted on the brake pedal, pretty easy to find and get too, but that couldnt cause it to blow bulbs.