Headlight wipers and washers
9.5.3 Headlight wipers and washers
9.5.5 Brake lights
There are two ways in which headlights are
cleaned, first by high-pressure jets, and second Figure 9.21 shows a typical brake light circuit. by small wiper blades with low-pressure water
Most incorporate a relay to switch the lights, supply. The second method is in fact much the
which is in turn operated by a spring-loaded same as windscreen cleaning but on a smaller
switch on the brake pedal. Links from this circuit scale. The high-pressure system tends to be
to cruise control may be found. This is to cause favoured but can suffer in very cold conditions
the cruise control to switch off as the brakes are due to the fluid freezing. It is expected that the
operated.
wash system should be capable of about 50 oper- ations before refilling of the reservoir is neces- sary. Headlight cleaners are often combined with
9.5.6 Electric horns
the windscreen washers. They operate each time the windscreen washers are activated, if the
Regulations in most countries state that the horn headlights are also switched on.
(or audible warning device) should produce a uni-
A retractable nozzle for headlight cleaners is form sound. This makes sirens and melody type often used. When the water pressure is pumped to
fanfare horns illegal! Most horns draw a large the nozzle it is pushed from its retracted position,
current so are switched by a suitable relay. flush with the bodywork. When the washing is
The standard horn operates by simple electro- completed the jet is then retracted back into the
magnetic switching. Current flow causes an arma- housing.
ture to which is attached a tone disc, to be attracted towards a stop. This opens a set of contacts which disconnects the current allowing the armature and
9.5.4 Indicators and hazard
disc to return under spring tension. The whole pro-
lights
cess keeps repeating when the horn switch is on. The frequency of movement and hence the funda-
Direction indicators have a number of statutory mental tone is arranged to lie between 1.8 and requirements. The light produced must be amber,
3.5 kHz. This note gives good penetration through but they may be grouped with other lamps. The
traffic noise. Twin horn systems, which have a high flashing rate must be between one and two per
and low tone horn, are often used. This produces a second with a relative ‘on’ time of between 30
more pleasing sound but is still very audible in and 57%. If a fault develops this must be apparent
both town and higher speed conditions. Figure to the driver by the operation of a warning light
9.22 shows a typical horn together with its associ- on the dashboard. The fault can be indicated by a
ated circuit.
distinct change in frequency of operation or the warning light remaining on. If one of the main bulbs fails then the remaining lights should con-
9.5.7 Engine cooling fan
tinue to flash perceptibly.
motors
Legislation as to the mounting position of the exterior lamps exists such that the rear indicator
Most engine cooling fan motors (radiator cool- lights must be within a set distance of the tail
ing) are simple PM types. The fans used often
Electrical systems 213
Figure 9.19 Indicator and hazard circuit
Brake lights
Ignition switch
Brake light relay
Brake light switch
Figure 9.20 ‘His Rear Lights’ (old Desmond Decker song)
Figure 9.21 Brake light circuit
214 Advanced automotive fault diagnosis have the blades placed asymmetrically (balanced
When twin cooling fans and motors are fitted, but not in a regular pattern) to reduce noise
they can be run in series or parallel. This is often when operating. Figure 9.23 shows a motor in
the case when air conditioning is used as the position.
condenser is usually placed in front of the radia- tor and extra cooling air speed may be needed. A circuit for series or parallel operation of cooling fans is shown in Figure 9.24.