1.8L 16V coolant sensor?

First off, this NG has the absolute best group of people in the entire system. I recently asked a question of the Mazdah group and I'm sure the car will rust away before the question gets answered. I hate Mazdah's. Wifes car. Anyway, my question here is that on the 1.8L 16V, when one looks at the side of the head from the drivers side, there are 2 sensors. The one on the left is the coolant temp. and the one on the right, to the right of the coolant hose is a what? It has no wire going to it, looks just like the coolant sensor and everything works fine i.e.: fan, gauges, cold start valve. I have owned the car since new in '89 and it's always bugged me. Thanks, Rick