In older telco gear they used fuses that were basically a spring held down with fuse wire, that when blown, made contact with the fault circuit. They effectivel

In older telco gear they used fuses that were basically a spring held down with fuse wire, that when blown, made contact with the fault circuit. They effectively where a fuse activated switch. When doing the led across the fuse trick, you need to make sure that the few mA passed is not harmful.