I have a mariner oil injected 45 hp. I don't have any spark.
I'm an auto mechanic but don't have any experiance with outboards and no manual can you give me some help?

First, check the lanyard switch at the control box.
Small red toggle switch. Make sure it`s in the run position. If you still have no spark disconnect the black/yellow wire at the switch box (ignition module).
If you have spark the problem is in the key switch or the lanyard switch. If you have no spark the problem is in the ignition system.
In order to troubleshoot it you will need a peak reading volt meter (Stevens mod. #CD77 or equivalent) and a spec.