Sue,
I agree with others above - you have a wiring problem, not a controller problem.
You have a direct short across the right turn signal output and the controller output. The controller output goes directly to the trailer brakes and has nothing to do with the brake or turn lighting. Your right turn signal is powering up the output side of the controller causing brake action and the controller indicator to flash on and off.
It's most likely in your truck. I would check the following:
- Take apart the wiring receptacle in the bed of your truck and look for poor wiring across the contacts installed by your Dealer
- Check the connections where the Dealer T-tapped your factory hitch wiring to install the receptacle in the bed of the truck
- Finally, remove the electrical cover from the pin box on the Monty and check the connections there
Those are really the only places the brake output and turn signals ever cross paths.