Why does fuse number 63 keeping blowing on 2000 Ford Focus estate?

The primary purpose of a fuse is to help protect a circuit from damage in the event of a short or overload. The fuse is protecting the wiring as well as the device. The primary reason a fuse fails, for at least a second there was a short circuit to ground that caused the fuse to blow. Always replace failed fuses with the proper amp fuse, not doing so can result in electrical system damage. Possibly you have too small a fuse installed. Always replace fuses with the manufactures recommended amperage. If the new fuse blows immediately you have a shorted circuit somewhere in that wiring system. The most common cause of a short tends to be when a piece of wire has a small exposed area that is bare. This piece of bare wire can often rub against metal and create issues for the electrical system because of the sudden surge in electrical current. While there can be numerous causes for a blown fuse, the majority of the causes of a blown fuse tend to be quite simple to repair. Once the failed wire is located the solution usually takes only a few moments to correct. Usually something as simple as repairing a bare wire. The other reason a fuse may blow is because the circuit is overloaded. This would happen if you have added accessories to the circuit. Of course a short in the device the fuse protects will cause a blown fuse.