RX892

I am wondering how to diagnose if it's the harness, torque sensor or something else. I want to take it to the dealership but I fear they will just tell me I need a new steering Rack. I don't know my way around the RX8 that well but I am mechanically inclined I was wondering what I could do to determine the problem. My power steering will come on sometimes but while I'm driving It cuts out and jerks the wheel and makes me quite nervous I won't go on the thru way when the power steering is on. Any help would be appreciated this has been an ongoing problem for me I have paid my Mechanic to clean the connections twice now it worked but didn't even last a month.