Post a schematic if you have it, and a link to your particular system.
If the fuse runs on 120vac you could substitute a 120v 7-1/2w incand. bulb for the fuse; this will pass some current so maybe you could trace the energized wiring up to the short. Measuring the voltage across the bulb will give you some idea of whether this a dead short or just an overload.
How quickly did the new fuse blow out after power was applied?