warning light, sometimes known as the no-charge light, is one
of the most important lights on your
. It warns you when the car's
is not charging the
In general, if the charging system is working normally, the warning light
should glow when the ignition is switched on and then extinguish when the
is started. But the light does behave in slightly different ways
depending on the type of generator fitted to your car.
If your car is equipped with a dynamo it is normal for the light to flicker
at idling speeds as this type of generator produces little or no
engine speeds. The light should extinguish when the engine speed is raised.
If your car is fitted with an
the warning light should not come
on when the engine is idling, provided the idle setting is correct, because an
alternator produces current even at low speeds.
There are three basic problems that an ignition warning light can develop.
First, the warning light bulb may fail to illuminate when the ignition is
switched on and the engine has not yet been started. (This is usually the
simplest to fix.) Second, the warning light may fail to go out when you raise
the engine speed. Third, the light may behave normally at low revs but then
come on at high engine speed.
If the warning light fails to illuminate when the ignition is turned on,
there are two possible causes.
One is that the warning light bulb may simply have blown. This could be due
to old age. The other possibility is a fault in the charging
- if the
generator is overcharging it may cause the bulb to blow. You can make a simple
check to find out which is at fault.
Warning light wire
To make this check you will need to find the warning light wire in the
engine bay where it connects to the charging system. But first you need to know
exactly which type of charging system you have so that you can identify the
Cars fitted with a dynamo have the warning light wire connected to a remote
, often mounted on the bulkhead or inner wing. Look on the
regulator cover for the
marked either WL or IND - this is the wire you
If your car has an alternator, the warning light wire connection depends on
whether the alternator is fitted with an internal or an external voltage
If the alternator is fitted with an internal regulator, the wire you want
connects directly to a terminal on the back of the unit marked WL or IND. If
the alternator has an external regulator, the warning light wire attaches to it
in the same way as a dynamo. Again the terminal will be marked WL or IND.
Some cars, however, have an alternator which uses a separate
warning light circuit. In this case you should disconnect the wire from this
Warning bulb check
Remove the warning light wire and touch it to earth. Turn the ignition
on and observe the warning light. If it illuminates suspect a charging
fault. If not suspect a blown bulb or faulty wiring.
For a dynamo, the warning light wire always runs from the light to a
separate voltage regulator. On an alternator the wire may run to an
internal regulator, to an external regulator or to a
Fitting a new bulb
To change the warning light bulb you will need to gain access to the rear of the dash.
On older cars this is usually quite easy as the bulb can often simply be pulled out of its holder by reaching around the back of the dash with your hand.
On newer cars the bulb is often located in the instrument cluster and connected to the wiring via a multi-plug connector and a
When fitting a bulb to the cluster unit, make sure it has a good contact with the metal strips in the printed circuit — it is quite easy to misalign them.
Disconnect the warning light wire and make sure the terminal connections are
clean and that the wire
tightly. If the terminals look dirty or corroded,
clean them up using wetor-dry paper, reconnect the wire and test the light
If the light still fails to illuminate, disconnect the wire again, turn the
ignition on and earth it to the bodywork or
If the light now illuminates, the fault lies in the generator or the voltage
regulator. If the light still fails to illuminate, you will find that the
warning bulb has blown or the wiring is faulty.
Warning light on
If the warning light fails to go out when the engine is revved, the fault
may again lie in the generator or in the warning light circuit.
A simple check you can make to find out where the fault lies is to start the engine and turn on as many
electrical components as possible. Now rev the engine and look at the
. If the lights noticeably brighten, the charging system is working
and the problem lies in the warning light circuit.
One possibility is that the warning light wire is being earthed somewhere
along its length. Check this by turning on the ignition and disconnecting the
warning light wire. If the warning light stays on, the wire is earthing
somewhere. Inspect the wire for any chafing against the bodywork and repair it
with insulating tape. If the wire is completely severed or badly chafed it will
need replacing with a whole new section.
The third possible problem with a warning light is that it goes out as
normal when you rev the engine slightly but comes on again as the engine speed
is further increased.
If the warning light simply glows dimly it usually indicates the problem is
somewhere in the warning light circuit.
Test this by switching on more and more electrical accessories once the
light has started to glow. If high resistance is the problem, the warning light
will become brighter as you do so.
Carefully work your way through the entire charging system looking for loose
or dirty wiring connections causing the high resistance. Disconnect the wires
and clean up the terminals if they are dirty. Don't forget to check whether the
battery lead connections and engine earthing strap are still good.
Remember also to check the generator to engine mounting bolts. These provide
an earth passage from the generator to the engine and body, but because of
their exposed position in the engine bay they can become oily and provide only
a poor earth connection.
Check this connection by removing the mounting bolts. Clean away all traces
of oil and dirt then refit the mounting bolts, making sure they are tight.
Fitting a new wire
Disconnect the old wire from its terminals at either end. Strip back
from the new wire and lay the bared ends in the connector
terminals, then apply the solder.
Once the solder has cooled refit the wire alongside the existing loom,
taping it at regular intervals. Make sure it can't touch any hot or
High speed faults
If the warning light comes on at full brightness at high engine speeds, the
fault is more serious.
There are several possible causes. On a dynamo it may be damaged
or possibly faulty internal windings.
With an alternator the problem may be caused by a faulty rectifier, which is
usually situated inside the alternator unit. The unit will have to be removed
from the engine in order to be stripped down so the faulty parts can be
replaced where possible.
Check with your dealer to find out what replacement parts of the alternator
are available - you may find it cheaper and more convenient to buy an exchange
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Although you may not smoke, fitting a cigarette lighter inside your car
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Bosch distributors are found on many different cars and are generally very
reliable. But after a high mileage you may find that the engine isn't running
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but the car doesn't accelerate cleanly, the problem may lie in the distributor