where do you put power trim fluid on 1999 90 hp Yamaha outboard?

It has been awhile since you posted the question, hope you know by now. But, in case you dont, Trim the engine up all the way (if it will). look at the right side (starboard) of the Power trim unit while facing the back of the boat. you should see the Fill screw. it will look like a little reservoir and use CAUTION Could be under pressure. Must be all the way up or it will be under pressure.

Frank
February 2008