Thanks for the suggestions ... To answer some questions:
When I connect the trailer to my TV, everything works perfectly except the brakes. (The turn signals and side marker lights are fine.) After I had my Prodigy installed, the display screen would read "Sh," meaning it was detecting a short somewhere in the system.
Now, when I plug it in, nothing shows on the Prodigy's screen, other than the small red dot meaning it's receiving power. When I move the manual brake lever to the left, it reads "nc" for no connection. It's no longer even recognizing the trailer as connected.
In probing the various wires at the 7-way plug, I noticed that I'm getting 12v
of power from one of the connections coming OUT of the trailer. Is this normal? Am I just reading a fully charged battery? It seemed odd that I would have power flowing from the trailer into the truck ... (Could this possibly short out my Prodigy? Or, would it have to be flowing through the brake controller's specific prong to do harm?)
One other thing: the PO installed an electric jack. I noticed it has a black wire (with inline fuse) that goes into the 7-pin plug and is ganged up with the blue brake wire. I've made sure each has a good, solid connection (one on each side of the set screw) ... should this matter? I didn't think to just disconnect the jack wire and try the brakes that way. The jack works perfectly as currently connected, by the way.
When probing each prong on my truck's 7-way connection, I'm only receiving a faint glow when I touch the electric brake prong (with the brake fully depressed). My electrical knowledge is skimpy at best, so I believe I'm going to call the mobile RV guy ... I already have a number, and have talked to him before. I guess that's my next best option until spring comes around and I can finally take the trailer to the dealer for service.