External lights
9.3.1 External lights
tion of the signals present at the connector of each of the ECUs on the network. The data at
Figure 9.7 shows the rear lights of a Mazda 323. each node will always be the same on the same
Note how in common with many manufacturers, bus. Remember that much of the data on the bus
the lenses are almost smooth. This is because the
204 Advanced automotive fault diagnosis
Figure 9.7 Rear lights of the Mazda 323
reflectors now carry out diffusion of the light.
moving or about to move. They switch
Regulations exist relating to external lights. The
off when parking or headlights are
following is a simplified interpretation of current selected rules.
Rear fog lights
One or two may be fitted but if only one it must be on the off side or centre line of the vehicle. They must be
Side lights A vehicle must have two side lights each between 250 and 1000 mm above the with wattage of less than 7 W. Most
ground and over 100 mm from any vehicles have the side light incorporated
brake light. The wattage is normally as part of the headlight assembly
21 W and they must only operate when either the side lights, headlights or front
Rear lights Again two must be fitted each with fog lights are in use wattage not less than 5 W. Lights used in
Europe must be ‘E’ marked and show a
If front spot lights are fitted (auxiliary diffused light. Position must be within
Front spot and
driving lights), they must be between 400 mm from the vehicle edge and over
fog lights
500 and 1200 mm above the ground and 500 mm apart, and between 350 and
more than 400 mm from the side of the 1500 mm above the ground
vehicle. If the lights are non-dipping then they must only operate when the
Brake lights Two lights often combined with the rear headlights are on main beam. Front fog lights. They must be between 15 and
lamps are fitted below 500 mm from the 36 W each, with diffused light, and must
ground and may only be used in fog or operate when any form of first line
falling snow. Spot lamps are designed to brake is applied. Brake lights must be
produce a long beam of light to between 350 and 1500 mm above the
illuminate the road in the distance. Fog ground and at least 500 mm apart in a
lights are designed to produce a sharp symmetrical position. High level brake
cut-off line such as to illuminate the lights are now allowed and if fitted
road just in front of the vehicle but must operate with the primary
without reflecting back or causing brake lights
glare
Reverse lights No more than two lights may be fitted with a maximum wattage each of 24 W. The light must not dazzle and either be switched automatically from the gearbox
9.3.2 Lighting circuits
or with a switch incorporating a warning light. Safety reversing ‘beepers’ are
Figure 9.8 shows a simplified lighting circuit.
now often fitted in conjunction with
Whilst this representation helps to demonstrate
this circuit, particularly on larger vehicles
the way in which a lighting circuit operates, it is not now used in this simple form. The circuit
Day running Volvo use day running lights as these
does, however, help to show in a simple way how
lights are in fact required in Sweden and Finland. These lights come on with
various lights in and around the vehicle operate
the ignition and must only work in
with respect to each other. For example fog lights
conjunction with the rear lights. Their
can be wired to work only when the side lights are
function is to indicate that the vehicle is
on. Another example is how the headlights cannot
Electrical systems 205
Rear fog lights
9.3.3 Gas discharge lighting
Gas discharge headlamps (GDL) are now fitted to some vehicles. They have the potential to provide more effective illumination and new design possi-
Light
bilities for the front of a vehicle. The conflict
switch
between aerodynamic styling and suitable lighting positions is an economy/safety trade off, which is
undesirable. The new headlamps make a signifi-
Side &
tail lights
cant contribution towards improving this situation because they can be relatively small. The GDL system consists of three main components.
● Lamp this operates in a very different way
Dip/main switch
from conventional incandescent bulbs. A much higher voltage is needed.
Main beam ● Ballast system this contains an ignition and
warning
control unit and converts the electrical system
voltage into the operating voltage required by the lamp. It controls the ignition stage and run up as well as regulating during continuous use and finally monitors operation as a safety
Spot lights
aspect.
& switch
● Headlamp the design of the headlamp is broadly similar to conventional units. However,
in order to meet the limits set for dazzle, a more accurate finish is needed and hence more pro-
Figure 9.8 Simplified lighting circuit
duction costs are involved. Figure 9.10 shows a xenon lamp system.
be operated without the side lights first being switched on.
9.3.4 LED lighting
Dim dip headlights are an attempt to stop The advantages of LED lighting are clear, the drivers just using side lights in semi-dark or poor
greatest being reliability. LEDs have a typical visibility conditions. The circuit is such that
rated life of over 50 000 hours compared to just a when side lights and ignition are on together,
few thousand for incandescent lamps. The envir- then the headlights will come on automatically at
onment in which vehicle lights have to survive is about one sixth of normal power.
hostile to say the least. Extreme variations in tem- perature and humidity as well as serious shocks
Note: If there is any doubt as to the visibility and vibration have to be endured. Figure 9.11 or conditions, switch on dipped headlights. If
shows some lights employing LEDs. your vehicle is in good order it will not dis-
LEDs are more expensive than bulbs but the charge the battery.
potential savings in design costs due to sealed units being used and greater freedom of design
Dim dip lights are achieved in one of two ways. could outweigh the extra expense. A further The first uses a simple resistor in series with the
advantage is that they turn on quicker than ordin- headlight bulb and the second is to use a ‘chopper’
ary bulbs. This time is approximately the differ- module which switches the power to the head-
ence between 130 mS for the LEDs, and 200 mS lights on and off rapidly. In either case the ‘dim-
for bulbs. If this is related to a vehicle brake light mer’ is bypassed when the driver selects normal
at motorway speeds, then the increased reaction headlights. The most cost effective method is
time equates to about a car length. This is poten- using a resistor but this has the problem that the
tially a major contribution to road safety. LEDs resistor (about 1 ⍀) gets quite hot and hence has to
as high level brake lights are becoming popular
be positioned appropriately. Figure 9.9 shows a because of the shock resistance, which will allow typical modern vehicle lighting circuit.
them to be mounted on the boot lid.
206 Advanced automotive fault diagnosis
cuit
Complete lighting cir
e 9.9 Figur
Electrical systems 207
Figure 9.10 Xenon lighting
Figure 9.11 Adaptive lighting using LEDs
Heavy vehicle side marker lights are an area Refer to Chapter 2 for further details about ‘volt of use where LEDs have proved popular. Many
drop testing’. A simple principle to keep in mind lighting manufacturers are already producing
is that the circuit should be able to supply all the lights for the after market. Being able to use sealed
available battery voltage to the consumers (bulbs, units will greatly increase the life expectancy. Side
etc.). A loss of 5 to 10% may be acceptable. With indicator repeaters are a similar issue due to the
all the switches in the ‘on’ position appropriate to harsh environmental conditions.
where the meters are connected the following readings should be obtained: