I have just edited a wiring diagram for the 1988+ Ninja EX250. I have made this diagram easier to follow and added some detail.
This is version: US 0.3 (my version of the diagram)
As you can tell it's still in its very early stages as cannot be compared to my newer diagram for the 2008+ 250r, in terms on quality, posted here.
http://www.ninjette.org/forums/showthread.php?t=35886
Eventually, I will update this diagram to make it as best I can for you folks who need to troubleshoot or mod your bikes.
If you have ANY requests or suggestions, please leave a comment here and I will look into them and possibly update the diagram.
Here is a link to the diagram.