Yet another old thread brought back to life...
We installed a Hayden transmission fluid cooler in my 04 GT this past weekend. The kit did not come with the right connectors. The instructions called for Hayden kit 252, or something like that and we drove all over town to find one. Then it still didn't fit. *sigh* For now, we bypassed the stock cooler.
YtnGT: Where did you get those connectors?
PS. For anyone else wondering, the line connected to the top side of the stock cooler is the line that feeds back to the transmission. I have transmission fluid splashed into my engine bay to prove it. This is for a 2004 Mustang GT.