I have been trying to get a kill switch that would work for my quad with no success,till I found this one.
It took me a little longer then I was expecting to figure out how to hook this up but with the help from my OEM repair manual I got the job done and it works great.
Because your YFZ450 uses a battery, the circuit is normally closed.
Warning: Ensure that you purchase the correct kill switch! To discover which type of switch you will require, please consult your Service Manual, contact your dealer, use the Switch Testing Procedure below, or consult the Model Compatibility list at bottom. Installing the incorrect switch type can lead to serious damage to the ignition and/or electrical system making the vehicle unusable.
Warning: Always disconnect the power supply BEFORE you begin installation. Failing to do this could result in serious damage to the electrical system or serious, even life-threatening, injury to the installer.