Had a look at mine earlier,I could just see what looked like a shutter but there is a lot of “crud” in the keyhole,when I first bought it,you could hardly turn the ignition key and I was half afraid I was going to twist or break it.I took off the chip sensor and tried to lever up the small plate and saw that the shutter was there and would move a little.Squirted just a touch of penetrating spray around the top and it started to move,I kept trying with no avail,the shutter looks very marked and pitted so I have given up as I didn’t want to damage the switch.I will keep my eyes open for an old S/H switch as it will come to pieces easily to change just the shutter assembly.Thanks for the replies team.