Short the wire and then look for the fuse that is burned out. The other way is to pull all the fuses out one at a time and check the wire with a test light to see if it is still live. When the wire goes dead, that is its fuse. When it comes to electrical work, you either know how to do it or you don't. Unfortunately, if you make a mistake, it has to be corrected with new parts. For what purpose do you need to know exactly what fuse and its amperage? If it is for a LED work light, they draw very little, and you are safe most of the time just wiring it into the system.