Look at the right side of the engine, rear bottom.  You will see a single wire entering the bottom of the engine.

To change it you have to remove the exhaust, right footpeg/brake assembly and remove the right side engine case.

Before you decide to replace it, you should visually inspect the wire, and then unplug the wire at the connector under the tank.  The switch should provide a connection to ground in neutral - and be an open circuit when in any other gear.