On a 1997 Yamaha Warrior with the original frame it is located on the frame bar underneath the motor, and a few inches in front of it. If it has a replacement frame, it may not have a vin, because on a replacement frame they are supposed to be cut out of the original frame and welded to the frame bar underneath the rear fender on the passenger side of the quad.
yamaha warrior 1989 vin # location
1997-2001
yes the crankshafts are the same
17
2004... the tenth digit tells you what year it is... there is a chart here http://forums.atvconnection.com/yamaha/315326-how-determine-model-year-yamaha-warrior-350cc.html
According to the online manual it should be on lower frame on left hand side.
on the left side, bottom frame rail, just under the engine in front of the foot pegs
year and model yamaha vin 510203147
year and model yamaha vin 510203147
When sitting on the seat it is under the left foot rest on the frame rail under the engine
According to the parts man at Yamaha who I talked with today, the number is on the frame on the left side by the footpegs. This was for a Warrior 350, but may work for your model too. For my Yamaha Moto-4 350 - the VIN is located on the frame, adjacent to the (rear side) of the left front tire.
For a Ngk plug it is a: NGK DR8EA