How to Manage non-IT Boss/People

Managing Non IT Boss/ People:

I am working in a Engineering company from last 3 Years as IT Manager. It has been tough journey since i jumped to this Industry from software development. Everything wents wrong on there end they blame it on the system. Till now i have been proving them wrong. Now i feel like giving up.
My problem is i am very straight forward. If they do wrong i do not hesitate to tell them. This puts me in trouble.
Pls. Help how to deal with it.