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The purpose of headlights being provided in a car is to produce illumination at night, considerable distance ahead of the vehicle. Ideal road illumination by the headlights should provide enough visibility for the driver without interfering with the vision of the other drivers of oncoming vehicles on the road. It is therefore imperative that the headlight meet these requirements. In this lesson we will look at the procedure for checking and setting the headlight beam.


Objectives After going through this lesson, you will be able to: Check and set the headlight beam Replace the headlight bulb

i. ii.


Two-filament Modern Headlight

This type of headlight uses two-filament bulb with a fixed reflector. In this case one filament is meant for the dipping beam and the other, the main beam filament is beneath it and it is located at the focus of the reflector. This method gives a driving beam of high intensity and a dipped beam of low intensity just below the horizontal level of the headlight centre. Further, a good spread of light is also obtained across the road.

7.2 • • •

Checking the Headlights Check the headlight switch for proper working. Check at the low beam and the high beam setting. Check the couplers that connect the switch with the lights.

If a headlight is not working properly, the headlight fuse should first be checked. The fuse box is mounted under the dashboard towards the right side. • • • • •

Remove the top cover of the fuse box. Remove the right side and left side headlight fuse one by one. Check that the headlight fuses on both sides are passable. Replace the fuse with another one of the same ratings if it is blown. Fix both the fuses. Install the cover of the fuse box. If the fuse is found to be acceptable, the bulbs are checked next.

• •

Pull the socket from the bulb. Check the socket visually for any carbon deposit etc.

• • • • • •

Check the reverse side of the socket for proper wire connections. Remove the rubber dust cap. Remove the spring clip Remove the bulb from the headlight. Check the bulb visually for any damage or breakage. Check the filament of the bulb for continuity by impressing battery voltage across its terminals.

The filament of the bulb is checked for continuity by taking tak a piece of wire and an touching one end of the wire to the negative terminal of the battery. The B terminal of the bulb is touched with the positive terminal of the battery and the other end of the wire is connected to the high beam terminal of the bulb. The filament is in an acceptable condition if the bulb lights up and glows with the full specified intensity. The other end of the wire is then connected to the low beam terminal for checking the low beam filament similarly. • • • • •


Place the bulb in its holder and clamp it in place. Mount the dust cap. Push the socket onto the terminals of the bulb. Recheck the functioning of the headlight at low beam and at high beam. Close the bonnet.

Checking and Setting the Headlight Beam B

ethod 7.3.1 Conventional Method • •

Adjust the air pressure in all the four tyres to 1.8 kg/cm2. Move the car to a flat surface and set set the car by pushing it up and down.

Fig. 7.1: Checking the headlight beam by conventional method.

Headlights of a car can be set by throwing the headlight beam onto a wall at a measured distance from the headlight and checking that it falls within the specified area. This procedure, however, requires a lot of space as the distance between the car and the wall should be ten meters. 7.3.2 Headlight Aligner A headlight aligner is used to set the headlights as it does not require much space. Headlight aligners are generally simple machines that only indicate ‘Pass’ or ‘No-pass’. When a headlight aligner is used, it is first set according to the procedure prescribed by the manufacturer. It should be set parallel to the car with the eyepiece at the same level as the headlight and the distance of the headlight from the aligner should be 50 cm. • •

Set the distance of the aligner from the headlight equal to 50 cm with the help of a measuring tape. Put the headlight ON and see its projection on the screen of the aligner.

Fig. 7.2: Headlight aligner.

The low beam as well as the high beam should be checked and the projection should be within the range marked on the screen. This ensures that the road will be well lighted in the dark and at the same time, drivers of vehicles coming in the opposite direction will not be blinded by the dazzle of the headlight of this car. If the beam of the headlight is not aligned properly, it should be aligned with the help of the 3 screws by which the position of the headlight can be adjusted. The headlight of the car can be moved up, down and sideways by screwing these screws in or out. • •

Check again with the aligner after setting the beam. Fix the beading and the front grille in their places. The headlight beam on the other side is checked in a similar fashion.

Self-check Questions 1. 2. 3. 4.

Why is headlight alignment necessary? Why a headlight aligner is used to set the headlights? If a headlight is not working properly what should be checked? The headlight is composed of how many elements?


Class Assignment

1. Discuss the need of aligning the head light.



1. Set the headlights of a vehicle by throwing its beam on the wall as per manufacturer’s specification.


Summing Up

In this lesson we first studied the procedure of checking the headlights and diagnosing the probable fault(s), if any, by checking the headlight connections. Next we studied the procedure of setting the headlight beam by the conventional method and also by using a headlight aligner. Proper illumination of the road is necessary for road safety. Hence the headlight beam should be set as per method prescribed by the manufacturer.


Possible Answers to Self-check Questions

1. So that headlights provide enough visibility to the driver without interfering with the vision of the other drivers of oncoming vehicles on the road. 2. It requires less space and is fast, accurate and simple. 3. fuse and bulb 4. 2.


Terminal Questions 1. Give the procedure of checking headlights in the conventional manner. 2. Give the procedure of checking headlights using a headlight aligner.



1. Maruti 800 Service Manual 2. User Manual: Head Lamp Aligner (Model HLA-1000). Manatec Electronics, Pondicherry.

7.10 Glossary Bulb

It is an electrical device fitted with wire type filament in a glass case and filled with an inert gas. When electricity flows through the filament it gives out light.


A protective device in a circuit which prevents circuit overload by breaking the circuit when a specified amount of current flows through the circuit. It is of wire or strip kind. Now blade type fuse are used.


An assembly with reflector and glass cover (lens) with replaceable bulbs. Headlights are mounted in the front of a vehicle and when switched on beam light in front of the car for road illumination.

Headlight aligner

It is a device to check and set the headlight beam for proper illumination and prevent dazzle in eyes of drivers of oncoming cars.

High beam

When the light beam from headlight falls at a considerable distance from the car it is known as high beam and used on highways.

Low beam

When the light beam from headlight is focused at short distance from the car it is known as low beam and used for city driving.