I don't have a wire diagram, but I can help with the other questions. Your 250 does not have a counter balancer so you don't need to worry about that. Only the 400 two strokes have a servicable counter balancer. Here is a link to a "how to" on adjusting the injector pump. Just a note on the pump. They do not use very much oil, but it's a good idea to make sure it's within specs every once in a while.
Plaris 250 Injector pump adjustment