1. Old fuse
2. 2 wire Cable 
3. LED lamp
4. 560 Ohm resistor
5. 2 way electrical block
6. 5Amp fuse wire

The cables can be jammed into the fuse holder, I soldered them in.

You don't have to use the Led & Resistor. An ordinary 12 volt lamp will do instead.

While fault finding, 'wiggle' components or cables to determine where the lamp turns on. That will be the location of the fault, which causes the fuse to blow.