99 Taurus coolant leak

Coolant leak at the Thermostat housing. Figured the Thermostat was bad so I am trying to replace it. I couldn't get a good look at it before it came out and now I can't remember how the new one should go in. I know the spring goes in first but does the o-ring go on that end or the other end? Does the position of it matter? Could the housing be bad?

There has been no indication of over-heating. The low coolant light came on and in a parking lot I saw a constant drip from the right side of the car located at lower part of the radiator.

This entire system is new to me, I'm used to the upper hose going to the thermostat which would be located at the engine and a lower hose connecting at another part of the engine but this is a whole network of hoses.

normally the t-stat will ride on a small ledge on the motor side or the neck side.Make sure to clean that ledge so the t-stat fits well.After fitting the t-stat Place the gasket over the piece that holds the t-stat and install the neck to the motor.