Radiator light on dash wont go off

My dash light came on and normally (well actually with in the last two months) I have checked the coolant tank and most of the time there is proper amount levels in the coolant tank so I would just disconnect the wiring that went to my coolant tank. (The one on the side of my engine above the right wheel well) and wait a couple seconds than plug it back in and the light would go off and stay off. Well its not working anymore so I went and bought the fuse and replaced it and the dash light still wont go off. In the last year I have replaced the radiator, the water pump and thermostat. I honestly don't know what it can be. I am not leaking any fluids anywhere and my car doesn't over heat. How ever though I have noticed that I can drive my car for hours and still be able to touch my cap on the radiator coolant tank and its never hot I can take it off if I had to. So I am puzzled and really could use some idea on what the problem could be