Looking in my GPZ500/ER5 manual a common theme is a Neutral switch (on the gearbox I guess) and a clutch switch (wonder where that could be??).
The neutral switch should be a wire coming out at around 7 -8 o'clock from the sprocket centre. They suggest disconnecting the wire to see what happens, and also removing the switch, the putting it back in without the sealing washer to check if that makes a difference. If removing the sealing washer works, then the plunger is worn and you need a new switch - do not ride it without the sealing washer! Put it all back together until you get the replacement part.
That's all I got, you're on your own from here
