Are you talking about the factory connector on a truck without factory installed receiver?

i'm guessing you might be referring to the 4 pin square connector that is (i think) behind the bumper?

If so, you do need to get a harness along with the hitch setup. the connector under the bumper is not meant to connect to the trailer...

If this is what you are talking about, you need something like this:

http://www.courtesyparts.com/Merchant2/m...ode=24167-00001

In addition to the hitch receiver itself.

I bet if you trace out what you had on your old X, it connects to something simular. The part number showed above is the same for 2005 and 2000-2004.

(NOTE: I'm "hitch shopping" right now - have not actually done the install yet)