The protection of the vehicle's electrical circuits is provided by a combination of fuses, circuit breakers and fuse links. A blown fuse can be easily distinguished from a working one by examining its transparent plastic housing. Carefully inspect the fuse to determine if it has blown. If the fuse looks normal but you still suspect that it is faulty, check the conductivity between the blade terminals protruding from its housing.
When replacing fuses, make sure that the replacement fuse matches the old one by type. Fuses rated for different amperages may look identical, so pay special attention to the markings. Replacing a blown fuse with one rated for a lower - and especially higher - amperage is undesirable. Each electrical circuit requires a different degree of protection. Make sure that the markings on the fuse body correspond to the amperage for which the corresponding circuit is rated.
If the replaced fuse immediately blows, it is not wise to continue replacing it. The cause of its blowing should be identified and eliminated first. In most cases, it is a short circuit in the circuit wiring caused by a break or damage to the wire insulation.
Original publication posted on the website BMWMan