1985 Dodge Truck brake fuse blowing

Unplug the brake light switch and see what happens. I'm trying to find a diagram to see what else is fed by that fuse. If you have cruise control, try unplugging the servo too. It is common to use the brake light fuse to power the cruise control because it needs to get a cancel signal when you press the brake pedal. With the blown fuse, the cancel signal is never coming, so if this is the power supply too, the cruise won't work. If the fuse didn't blow until you pressed the brake pedal, I would suggest looking for a chewed up trailer wiring harness.

Caradiodoc