Ever see a partially burnt fuse?

[Longshot270]

It was the first time I've ever seen anything like it. I was making some wire adjustments on the harness for my new stereo head unit and the accessory wire slipped and sparked with the 12v hot wire. Next thing I know nothing works right. Neither the new head unit nor the old one would do anything. I get my little hot/cold tester with just an LED light and it worked. Hooked everything back up and nothing worked. Got out my fancy digital volt meter and the 12v hot wire read 1.58 volts. I kept rewiring the harnesses and again my fat fingers lost the hot. This time when it sparked I retested and the wire was cold, checked the box and found the 20 amp fuse had been blown. Didn't have any extra 20 amp fuses so I used a 15 amp. Now everything works again. Just thought it was strange that a fuse could only burn part of the way.