First find out what kind of fitting and rating the bulb you need to replace is. Ratings are measured in watts, and are usually found on the metal base or on the glass itself. Some cars have combined tail/stop bulbs.

These bulbs have a bayonet-fitting, with offset pins to ensure that the bulb is fitted the correct way round. Halogen bulbs that are used in headlights and front fog lights have an “H” number to identify their type. It’s a good idea to carry a set of spare bulbs in your car. Changing a halogen bulb differs from car to car, but here's a guideline for changing it.

1. First switch the headlights off. If the bulb has just blown it can be very hot. If there's a cover, unclip it from the back of the headlight to get to the bulb.
2. Pull out the wiring plug from the back of the bulb, and move the rubber cover from the back of the bulb.
3. Release the spring clip - squeeze its legs together and pull the clip away from the bulb holder,. Pull out the bulb.
4. Hold the new bulb carefully making sure you don't touch the glass with your fingers – use a cloth or paper tissue.
5. Halogens usually have tangs around their edge so that they can only fit in one position. Slide the new bulb in place, and then fix it securely it with the spring clip. Refit the bulb cover and reconnect the wiring plug.