tach/ac problem on 350SDL
 

The tach and ac clutch quit working on my 90 350SDL the posts say overload relay will do this so I checked it and it was ok. What reading should I be getting from flywheel speed sensor so I can check that as I am told that will shut the ac comp off also. Ac works fine when jumped from external power but no volts from eds. Anything else I should check and how?:confused: