Alternator available on 90 15msh yamaha?

The Pamphet for my 2009 2 stroke 15hp (15msh) says an alternator is optional. How do I order this Yamaha part and is it easy to install?
Thank You

[boats.net]

You would need the rectifier kit, part number 6G1-81970-00-00. Connect to two green leads(alternator leads) on motor to green wires on rectifier and connect battery leads from rectifier to battery.

[sailingmagnus]

Do I have to have a battery

I have 2007 15 MSH with the alternator already installed. I hooked the two green wires to the regulator and the output wires to a light. I am pull start, no battery. I just want an all around white light when the engine is running but I don't get any output with this wiring config. Do I have to have a battery for the regulator to work? Is there an option for a voltage limiter that works without a battery for my situtation?