2003 Expedition--Prodigy installation?

[Kistler]

I am going to change brake controllers--from Voyager to Prodigy and was looking under the dash on my 2003 Expy. There are two connections-one is a gray cube (right now it is being used for the Voyager) and then there is a black rectangular plug (not used, seems to be attached to the bottom of the dash) --by the way the gray cube is dangling What is the rectangular plug receptacle for?

 

[Wapiti]

Your Prodigy should plug right in where the Voyager was. You'll really like the Prodigy.

As far as the black rectangular plug, if it's the one mounted right under the dash and visible, that should be the one used for plugging into the vehicle's computer for diagnostics and programming.

I'm considering buying an Expy for towing. How do you like yours and how does it pull in the hills?