2000 Dodge Truck 3.9l blows fuse

There isn't much in that circuit. Unbolt the smaller wire from the starter, then see if the fuse still blows. If it does, follow that wire back to the starter relay to see where it is grounded. If it doesn't blow, something is shorted inside the solenoid or with the 1" braided cable between the solenoid and starter motor.

If the fuse still blows with the smaller wire disconnected from the starter, use a pair of spade terminals and jumper wires to connect a 12 volt light bulb in place of the fuse. If the brown solenoid wire to the starter is grounded, the light bulb will be full brightness when you turn the ignition switch to "crank". That will limit current to a save level, and you can move things around to see what makes the bulb go off. When it does, the short is gone.