OK, so I am up in the high Sierras and realize in the morning that the reason the heater fan in our trailer ran all night was that we were out of propane. Make a long story short, the batteries were about dead, but i didnt worry, I knew the hot lead from my truck would be ok. Wrongo! Halfway home, the electric brakes go out when the last of the trailer batteries juice goes. I HAVE NO POWER ON THE HOT LEAD! I checked all fuses, and cant figure out where to check next. HELP someone! All other functions in the wiring harness/connection seem to be fine...

 

Your going to have to give some more info, your problem is confusing. The trailer batteries have nothing to do with the electric brakes, now if the wiring harnes going back to the plug connection going to the trailer and either shorted out and caused the hot wire to go bad is one thing, they can come undone, some take some hunting down with a test light to find. Maybe someone else has some insight, Goodluck,,,Rick