You haven't specified the series of engine or it's year so we're all guessing a bit.
Read your handbook before you start. It should tell you.
If you are really stuck:
It is possible it is already recified. Follow the cables back from the connector. If they end up under the flywheel, it's likely ac. If they enter a wee pack of some sort and the exiting cables go up to the flywheel it's likely dc. Alternatively, set a multimeter to dc at a safe voltage and connect it to the output. If the output is ac, it'll read low or, if a digital meter, it wont settle. If the output is dc, then you should get a fairly steady highish reading.
If you conclude it's ac, as a final check, set the meter to ac and you should get a highish reading - guessing about 15-18v.
If it proves to be dc, then, as suggested, you need a battery.
It would be easier to phone Yamaha and ask them!