Brake lights out!

The brake lights on my 2001 Jeep Grand Cherokee are out completely. Tail lights and headlights work. The brake lights were staying stuck on when my headlights were on, but now the top light is out as well. I went to the dealership multiple times and after paying far too much $ each time, they tell me the problem was solved. The brake lights would work for a little bit after each repair, but would go out again. This last visit, they said it wasn't a fuse, brake switch, bad bulbs, but it is a short due to the hitch wiring or something and that I'd need to pay $2400 to replace the entire junction block box. Everyone else I've talked to says that can't be right. Please help!