My 97 crown vic keeps blowing the radio fuse everytime I open the trunk.
assuming you’re not concerned about a functional trunk light on an old vic, I would start by diconnecting the trunk light. If the fuse still blows check the wiring near the hinge point of tour deck lid. look for any bare wire or signs of arcing. Does this car have the electric latch? If so, There could be a problem there.
I would guess that radio fuse also powers something in the trunk, like the light. I am with tractorman on this one.