erm, Haynes manual showed me! It was a while back when I did mine - if I remember rightly, it's really easy to get at - gearbox is on the right of the engine as you look at it - the switch is located slightly towards the rear of it & you'll notice it has a wire coming from it. Like I said, it just unscrews (with a spanner) - if you have a nosey, you'll spot it. Failing that though, have a look in the Haynes manual (libraries have 'em if you've not got one). Unless someone on here can explain it better than me?