This is called a negative earth system, and when buying an electrical accessory a radio, for example check that it is of a type suitable for your car system. Fitting a radio with the incorrect polarity will damage the set, but most car radios have an external switch for setting the polarity to suit that of the car. Switch to the correct setting before fitting.
The fuses are usually grouped in a box or on a panel with a cover. Ideally, the box should be fixed in an accessible place — such as the bulkhead under the bonnet.
In a negative (-) earth-return system, the current flows from the positive (+) terminal to the component being operated. The component is earthed to the car body, which is earthed to the negative (-) terminal of the battery.
The current would encounter the resistance twice, and the double resistance would halve the current, so that the bulbs would glow only feebly. Connecting the bulbs in parallel means that electricity goes through each bulb only once.