The Tesla Model X comes with a new 13-pin female connector and most older trailers have a old 7 pin male connector.
You need to buy an adapter at Biltema or Jula. Here is the adapter you need
When you insert the adapter try to push the original lid behind the plastic bottom case as in the picture. This is the only way to get the adapter to fit the plug without the original lid getting in the way.
Once you have connected your trailer and hooked it up, go into the Tesla and make sure that Towing mode is on
Once you connect a cable the car automatically enters into “Towing mode” if it does not do this, go to: Controls->Driving->Towing Mode
Once you have on towing mode, go drive. You can use your rear view camera to keep an eye on your trailer