There are generally several fuses protecting various areas of the motorcycle. The main fuse has a heavier rating than all of the fuses that follow so that it will remain in place supplying current when a lesser rated fuse further down the system blows. Generally power from the main fuse travels to the ignition switch and then returns to the fuse box for distribution to all of the motorcycle's sub-circuits which may protect the horn and indicators, another the lights and yet another the brake lights. When a problem does arise it should be isolated to the area that it is in and not affect the running of other areas of the motorcycle.
At this point it is worth mentioning that is is very unlikely that there are two electrical systems that are designed the same since they are intended to serve the purpose of the motorcycle model for which they are designed. There are also changes for various reasons during a model run due, perhaps, to a change of component supplier or a modification for assembly reasons. Therefore, although manufacturers have common ways in which they approach design and similar components are often employed, it is best to consider that every wiring system is different and that it is very necessary to consult the relevant wiring diagram for a particular motorcycle and model. To this end you should find a wiring diagram in the back of the owner's handbook.
From te fuse-box power is supplied across the motorcycle to serve its many purposes. Sometimes this power may be supplied to a component then to a switch and from there to ground in order to complete a circuit. At other times power could be supplied to a switch and from there to the component and then to ground to complete the circuit. A good example is a warning light circuit where power can run from the fuse-box through the light to the switch is activated. Alternatively the power can run from the fuse-box to the switch, then out of the switch to the light, then from the light to ground and this circuit is completed when the switch closes the circuit between its two poles. This simple example of different ways to perform the same task applies to any and all components and all motorcycle manufacturers. Whichever way a particular electrical system is designed, the best way for all but the most experienced technician to solve electrical problems or to understand how their particular motorcycle's electrical system works is by consultation with the wiring diagram, the use of a test lamp or better multimeter and plenty of time and patience.
The most widespread reason an owner looks at an electrical system is when something has gone wrong. Some of the more common reasons are, firstly, to do with the battery. Loose or corroded terminals can cause unusual symptoms such as the warning lights going out and the starter not going when the button is pressed. This can come about from the terminals being able to cope with small amounts of current but not being able to cope with the sort of current required to operate the starter. At the same time these same symptoms could also be the sign of a dead battery or of one with a low electrolyte level.
Routine maintenance would ensure that two of these problems would not occur and, as for the worn-out battery. It can often come as a surprise, but be aware that old batteries often last very long but give up the ghost at the first signs of colder weather.
Because metal, moisture, and electricity make the perfect formula for corrosion it is important to prevent the build-up of moisture in switches joints and in the loom. Cleaning off corrosion and regularly applying a product such as battery terminal protector to suspect areas will assist in further prevention of problems. The last common problem that occurs with electrical systems on motorcycles is interference. Removal and replacement of looms will create problems if they are not put back exactly as they are found. The twisting and stretching of a wrongly fitting loom can cause broken wires and joints in places that would never normally be a problem and the effect of that can be that these problems are the most difficult to find.
Often this type of problem can eventuate from renovation or from smash repair. Therefore look for badly fitting looms and wires not tied back correctly – it may signal a motorcycle that is not quite what it is made out to be. Wiring looms are not designed for regular removal and nor are the plugs and fittings that go with them and these can suffer damage that may lead to faults occurring.
I am pleased to say that modern motorcycles have vast improvements in the quality of their looms, plugs and switchgear compared with their counterparts of just a few years ago, even if the requirements of a modern motorcycle put greater demands on the electrical system.