I believe it's a sensor installed inside the transmission on the valve body.
You can replace the outlet transmission line with an older model year which has provisions to install a sender. If you replace the line don't forget to remove the check valve from the trans. heat exchanger under the turbo, the older model transmission line already has the check valve in it. Do a search on it or maybe some one can jump in here and help. Adding a transmission gauge is the best thing you can do to watch your trans. and protect it before it's to late.
Fred.