on my inline six my rad is a 3 core closed system, and what i want to know is, on the left side of the rad just about half way down there is a large brass fitting that screws into the rad, with two wires coming out of it that are about 4-5 inches long with a connector on the end. Can anyone tell what this is and if it has anything to do with my jeep overheating. i thought that its was the coolant temp. sensor, am i right or is it something else

it is a tempature switch, sends a signal to the electric fan relay telling the fan to come on because the temp in the rad is to high. On my 89 I have the electric fan come on when ever the jeep is running when it is hot and humid, helps to keep the temp down in the summer.