What the $^% is wrong with my trailer brakes?

[Darel]

OK, I have a '97 with the factory tow brake setup. The only way the red light would come on would be if you stepped on the pedal and fingered the controller at the same time.
I figured the problem was in the controller, so I bought a Tekonsha Prodigy. It is wired correctly, all I did was cut the factory plug off the old controller and splice the harness for the Prodigy on it. Yes, I double and triple (then later cut off all my electrical tape and quadruple) checked the wiring. I get the red light on the display indicating the controller has a good 12V circuit. Supposedly, when I plug a trailer into the socket on the hitch, regardless of motion, I should get a "c" on the display. No "c". If I finger the controller I get "nc", which means no connection. When I finger the controller and step on the pedal at the same time, I get a blank display with just the little red light for 12V power. Basically, the controller isn't recognizing that I have a trailer back there. A test light on the plug confirms all this, I only get current when i finger and step simultaneously.
I have tried this on 4 different trailers, two less than a year old. Same results every time. I know the prongs in the 6-round plugs are matched up because like I said, the brakes used to work when I fingered the controller and stepped on the brake at the same time. What is the problem? The lady at Tekonsha Customer Service (who was really bitchy, by the way), basically confirmed that the controller is working properly and is hooked up properly. She wasn't any more help than that. The controller has displays for short circuits, overloads, bad grounds, and a couple of other common problems and it indicates none.
Please help! This problem has been driving me nuts for months!