If you mean the neutral light isn't working, it also works the start solenoid circuit. So, if the bike doesn't think it is in neutral, the starter solenoid won't work. Check that neutral light circuit. Neutral light also won't work if the battery is flat or main fuse blown, but then nothing else will work either (lights, horn, etc).

 

 

Yes, Yams are a bit prone to this, I've got a Kodiak in at the moment (broken UJ) and note that you have to wiggle the gear lever a bit to get neutral to light up. Most switches can be dismantled and the contacts cleaned.

 

Pull the clutch in while in neutral and it will start