2007 Mercury 90hp 2 stroke tach stopped working

I have a 2007 Mercury 90hp 2 stroke motor on a 2006 Tracker 175WT. Tach was working the last time I had the boat out. Had problems originally with the oil tank float. It was setting the alarm off. Replaced tank. All was fine. Took boat out again. It was hard to start. Once idling when I put it in gear it kept bogging and dying. Finally it took off. Everything else seemed fine but after a while the oil and hi-temp alarm started going off again but not loudly. Checked the connections, unplugged the oil sensor and the temp sensor and the alarm stayed on. At this time I noticed the tach was sitting at zero. Would not move with key on and engine running at all. I know the alarm is set to a ground so if something is grounding out it will start to sound. How do I check to make sure that my rectifier and regulator are working? I know that I am getting voltage and charging my batteries. Or is my stator not working right? I need to know what my next step is or how to check these things. I have a digital multi-testor but not sure what wires to check and what the resistance should be. I do not have a manual or electrical schematics for this motor.