Keeps blowing?
One bulb blowing isn't 'keeping' blowing, as has been said it could have been a bad bulb.
Was there a working bulb in it before? If not, are you certain the leads to the bulb are connect in the right place on the motor? It should be delivering 12v when correctly connected, but could be a lot more if it's wired incorrectly.
Also, any excessive vibration will shorten the life of a bulb.