Probably a short on the wiring mate, bulbs are permenantly earthed and have a switched feed to them. Take the plug off the stalk, take the bulbs out of the side that is blowing, and continuity test between Black/Green and Earth, and Black/White and Earth (sorry can't remember which side is which) one shouldn't have a continuity reading obviously. If they both do there is a fault on the circuit. If not probably the stalk.