How do you identify your boat motor i have an older 90hp mercury. how do i tell what year and model it is?

if it is not clearly marked on the cowel you'll have to call Mercury and have them source the serial number, while in the boat looking out the back on the center of your steering ram there will be a serial number as well as if you open the cowel and from same spot look back to the powerhead casting there will be another number on there witch you can source model and other info hope this helps