A halogen headlamp uses more power, but gives more than twice the illumination.
If the bulb is of the halogen type, it should not be touched with the fingers. Use a clean, dust-free cloth to keep fingermarks off it and avoid premature failure. Clean it with methylated spirit on a cloth if necessary.
Filament damage cannot be seen in a sealed-beam unit, and a different method is needed to check if it is faulty (see panel on right). Checks on wiring and connections must include the spring-loaded contacts, where that type of bayonet bulb holder has been used.
A sticking plunger could result in the failure of the lights in that unit, while failure of an insulating washer could mean a short circuit and a dimming of all the lights, or cause a fuse to blow.
A dim yellow light on one side is usually a faulty earth connection between the headlamp and the body of the car.
The connection is often simply a wire lead attached to the body; corrosion or dirt may cause a high resistance in the connection which results in a dim light.
Unbolt the connection, and use emery cloth to clean the terminal and washers. Use a wire brush on the bolt. Clean the surface of the metal where the hole is drilled. Reassemble and tighten firmly.
The same fault can occur on both headlamps when they are interconnected. However, when both lamps are dim, another possible cause is rust under the locating flange of one or both of the bulbs. Clean away dirt and corrosion wherever you find it.
Total failure of all the headlamps – both main and dipped beams on both sides means a failure in the feed to the main lighting switch or between that and the dipswitch.
Where there is a fuse fitted in the headlamp circuit, check it to see if it has blown (See Working on the wiring system).
Circuits can be overloaded by adding extra driving lamps, or installing bulbs that are too powerful in the main lamps. Another possible cause of fuses or lamps blowing is a faulty voltage regulator (See How to test a car battery) in the charging circuit.
Testing a sealed-beam unit