I have a 2006 F350 dually diesel, and every time I hook up a trailer and touch the brake it blows the fuse. I’ve had a new trailer plug installed and a new Brake controller in the dash. They said they couldn’t find anything wrong with the wiring.

 

Which fuse?

 

The fuse in the fuse box that’s inside the engine compartment. It’s a brand new trailer, so I know it’s not the trailer. As soon as I put it in drive, press the brake, it blows the fuse

 

If you depress the brake pedal in park, does it still blow the fuse?

Can you get any wiring info for how the trailer was wired?
If the truck wiring is not the same as the trailer wiring, somebody has their work cut out for them.

What we need to know to start,
Looking at the plug on the truck, not the cord, leave that off,can you verify which pin shows power when brake pedal is depressed.
If the truck shows one thing and the trailer requires another, that could be part of the problem.

Something else, is your cord wired directly to your truck or does the cord get plugged into the truck?

What is problematic here is so many people got involved and we don't know what they did so we have to start from scratch and verify each and every connection.

As a last resort, you may need to take the trailer to the people that installed the controller.