It feels like someone is flicking the engine kill

[Grahamm]

There is and it's shown in the FZ6 Haynes manual, but still involves lifting the tank and I can't remember if the airbox has to taken out as well.

I've just had a look at the Haynes manual and, yes, you need to take out the air filter housing too.

Once you've done that you need to disconnect the sensor sub loom wiring connector, then you can clip multimeter leads to the terminals and see if the resistance suddenly changes as you twist the throttle.