speedometer sender unit

[AyJay]

It's on the back of the gearbox, an inch or two above the swingarm pivot. If yours has died (mine did), contrary to what a dealer might tell you, you can get to it by without taking the swingarm out. You just need to unbolt the white overflow tank to get access. Mind you, it's still fiddly and a bit of a palaver, but half an hour will sort it.