in the bottom side of my koyo rad, there is a thread for a sensor. anyone connected their sensor there?

 

Same Sensor, same Rad. I've ditched It when I went with the Microtech LT8. It's a shame really, b'c I bought the Water Temperture Switch brand new 2 summers ago with all the other Water sensors.

Being that you have a s4, you not only have one but need It In order to not effect the operation of the ACV if the wires are left off. It's emission related in its function. If you have an aftermarket radiator with no sensor at the bottom left....then just join the two wire together in a butt splice.