ok gazza,the ignition switch is held on wih two shear bolts they need to be undone using a centre punch on the outside edge of the bots and knock it round anti clockwise to get the lock off the frame.i have managed to drill a very small hole up the centre of the lock before on an ay 5o which uses the same zadi lock,you can drill a small hole up the middle from the bottom of the lock once you have undone the two small cross headed screws on the bottom that hold the plastic switch part on.when you ahve drilled it you can use a thing pointed bit of metal like a strong needle and push the broken key part out.good luck with it as its a fiddly job
adam bike doctor, March 2010
