Larry,
I recently picked the Prodigy as my first ever brake controller for my first ever trailer-TM2720SD, after talking to some folks and checking out websites.  I ordered mine from Southwest Wheel (www.southwestwheel.com) for $124.95.  One of the reasons I picked that model was because I could get a Pocket Mount Kit (#7686) to allow me to use one controller in two different vehicles.  I ordered the GM harness for $8.50 even though I had a "factory harness" .  The factory harness has a plug-in connector on just one end and you have to splice the factory harness to the wires you get with your Prodigy (with it's own plug-in on the other end).  ( I plan to use that connector with my other vehicle harness when that vehicle arrives (company truck).  It took more time to figure out just where I wanted to mount the holder kit, mark and drill the two holes than connecting the wiring--it plugged in on both ends.

Have fun,
Tom