Free Auto Repair Advice by Certified ASE Technicians
First Things
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Taillights
No Taillights (Exterior, Running Lights) Taillights Out
Introduction:
Tail lights, exterior or running lights are lights that are positioned on each corner of
your car. These lights are used to make the car more noticeable at night by
staying illuminated while the headlights are on. The taillights can also be
controlled separately from the headlights if desired. Taillights can be used at
dusk or in the early morning to increase safety by helping other drivers to see
your car more easily. In some states it is required to switch on taillights in
foul weather including fog and rainy conditions. All headlight switches
have the option to turn the running lights on separately. When the tail
lights are activated the dash lights will also come on to alert the driver the
taillights have been activated. The brightness of the dash lights can be
adjusted by turning the rheostat connected to the headlight switch. This is done
by turning either the pull-out activation knob or the thumb wheel located above
or below the headlight switch bezel. Some manufacturers have located the dash
light illumination control remotely from the headlight switch, usually somewhere
near the instrument cluster itself. The running light circuit can be controlled
electrically through a BCM (body control module) or a LCM (lighting control
module). These computer controllers are designed to warn you that a bulb has
failed by illuminating a bulb failure warning light on the dash. If your car is
not equipped with either of these controllers the headlight switch will perform
the actual connection to complete the flow of electricity and illuminate the
running lights.
Tail Lights
The interior and exterior lamps are protected by separate fuses. Some cars have
a control relay to help shoulder the electrical load. Vehicles are either
designed to have the running light bulbs separate from the directional signals
while other manufacturers have integrated the running light circuit into the
directional bulbs. Much like the brake light systems in American cars the
running lights are integrated into the blinker bulbs, while Japanese and
European cars have separate lighting systems. Unlike the American and
Japanese/European car manufacturers brake light systems we will be able to test
the running light systems in all models in a similar manner. Vehicles that have
towing capabilities will have a separate wiring system to power trailer lights
that are protected by additional fuses located in the fuse panel or the under
hood power distribution panel. The rear license plate of the car is illuminated
by a small bulb which activates when the running lights are on. It is unlawful
to operate a car with any lights not working properly and must be corrected in a
reasonable amount of time. Some running light systems are equipped with a self
controlling timer that will allow the running lights to stay on for a
predetermined amount of time after the user has exited the vehicle. This safety
device can be disabled in most cases if this option is not desired. In this
section we will go over the common failures for the running light control
circuits and the simple repairs they will require to fix. Theses malfunctions
can range from one or all lights not functioning and we also will cover dimly
lit or flickering bulbs.
Before We Begin: Depending on the running light malfunction you
will need a new bulb and
test light with a possible wiring diagram which can be found in a car repair
manual. Also to aid connection problems a small piece of abrasive paper
(sand paper) can be helpful. When performing test wear protective gloves and
eyewear. (Note: Never connect power wires or terminals to ground, fuse
damage can occur)
Troubleshooting Procedures - Read Completely Before Beginning
All Taillights Not Working
- Step 1: Tail Light System Fuse Inspection - A fuse protects the
taillight circuit from damage. If the fuse fails it does not allow
electrical current to flow to the taillights. To inspect the fuse, locate the
taillight fuse that protects the circuit in the fuse panel. This panel could
be located under the
hood in the power distribution center or dash on the drivers side in most
cases. Connect a test light
clamp to a ground source like an engine accessory mount or dash bracket and
move the ignition key to the "on" position. Now with the test light, probe both
terminals of the fuse. If one terminal of the fuse illuminates the test
light the fuse has failed and replacement is required.
If the new fuse blows as soon as it is replaced or when the
taillight/headlight switch is activated the taillight circuit is shorted to ground
and requires troubleshooting to repair the damaged circuit. A system short
can occur, but rarely. If no power is detected at the fuse panel (either
side of the fuse) use a wiring schematic to trace the power source (wire)
and repair as needed. You will find usually when this condition occurs there
is a main power relay or fusible link that has failed. To find a wiring
diagram a car repair manual is required. When the test
light illuminates on both terminals the fuse is "ok" continue to the next
procedure.
- Step 2: Test for Power at Headlight/Taillight Switch - Once the taillight wiring has been located and the fuse
condition has been confirmed as ok, use a grounded test light and test for a
twelve volt power source at the rear of the headlight switch on one or two
of the terminals. (Note: sometimes a headlight switch wiring loom will be
the test point because the terminals are not exposed.) The reason for this
is to test for power present and available to be connected to the taillight
bulbs. The switch must have power to be able to supply power. If no power is
confirmed repair the fuse holder or the power feed wire from the fuse panel
to the taillight/headlight switch. If power is confirmed at the rear of the
switch turn the switch to the "on" position and test the remaining terminals
(or wires), power should be present at the remaining terminals if not, the
switch has most likely failed and requires replacement. If the headlight
switch tests ok continue to the next step.
- Step 3: Non-Relay Controlled Taillight Systems Only - This test
is for vehicles that are not relay controlled lighting systems (use no
taillight relay). Remove to expose one or all of the taillight bulb sockets.
Using a grounded test light test for power inside the bulb socket. Use
caution to not contact the side of the bulb socket with the test light
probe, this could cause a fuse to fail. If the test light does not
illuminate/power is not present on any of the socket terminals the wiring
circuit to the headlight/taillight has failed and requires
repair. For this a wiring schematic is required. Trace and test the wiring
and recheck system.
- Step 4: Relay Controlled Taillight System Test - Sometimes
manufacturers can design a taillight control relay to help shoulder the
electrical draw many bulbs can cause on a single circuit or to control the
circuit remotely like a BCM (body control module) for example; when the
alarm is activated the taillights will activate for a couple of seconds to
inform the user the alarm has been activated. When this wiring
system is implemented the headlight/taillight switch is used a the "trigger"
circuit and a taillight relay acts as the actual activation switch. To
perform a test locate the taillight control relay, usually a diagram
is located on the under side relay lid. Most relay control centers are located
under the dash or hood of the car. If you cannot locate the relay a car
repair manual can be used. If your car is not designed with a control
relay refer back to step 3. After the relay is located remove the relay from
the relay block or connector. With the key in the "on" position use a test
light to probe all connector terminals. Two of the terminals should have
power, and the remaining two or should be dead. If power is not
present at two of the terminals repair the fuse or power feed circuit as
needed. If power is present, remove the ground lead from the test light and
connect it to a power source for example the positive side of the battery.
Next, probe the remaining two terminals in the relay connector
while turning the headlight/taillight switch from "on" to "off"
and repeat. On one of
the terminals that is tested should blink on and off with the
headlight/taillight switch. If one of the terminals blinks the relay has
probably failed and replacement is required. If no terminals blinks the
control switch (headlight/taillight) has most likely failed or the ground circuit
connected to it.
One Taillight Bulb is Out
- Step 1: If one of the taillight
bulbs has failed the problem is probably the bulb itself. Remove the bulb
and inspect, check for any burned color or white with blue smoke inside the
bulb and replace with new if this condition is detected. If you have
replaced the bulb with a new unit and the bulb still doesn't operate remove
the bulb. With the bulb removed use a grounded test light to test the inner
contacts of the bulb socket. Be carful not to touch the test light lead to
the outer socket ring for this could cause a fuse failure. If power is
detected connect the test light to a 12 volt power source such as a positive
battery terminal. Use an extender wire if the test light lead is not long
enough. Connect the test light to the bulb socket it should light up. If not
the bulb socket ground had failed and repair is required. Note: it is common
for bulb sockets to fail due to the heat they are exposed too.
Dull Tail Lights
- Repairing Dull Taillights: Dull
or dim taillights are a dangerous to other drivers because it hinders the
ability to see your car when daylight is at a minimum. Because the taillight
bulb is working, just not correctly it can be a mystery for most people to
comprehend why this condition is occurring.
The fist step is to remove the bulb and confirm the correct bulb is installed.
Then, turn
the ignition key to the "on" position and activate the
headlight/taillight switch.
While the taillight bulb is installed touch a grounded test light to the outer ring
of the bulb socket. If the bulb brightness increases the bulb socket ground
has corrosion that must be cleaned or in some cases the bulb socket will
need to be replaced.
How to Repair Flickering Tail Lights
- Taillight Bulb Repair Guide: A running
light that flickers can be distracting to other drivers. Flickering lights
occur because
the power or ground source is being disconnected momentarily. Common causes for
this condition is a loose fitting bulb inside the bulb socket. To test for this condition
expose
the taillight bulb in question. Next, switch the taillight on and move the
taillight bulb around slightly in the bulb socket. If the bulb flickers repair the bulb socket
or replace the bulb to regain proper taillight bulb operation.
If the taillight circuit flickers (all bulbs flicker) wiggle the taillight fuse and
associated wiring
at the taillight socket, headlight/taillight switch.
High Amperage Failure
- Testing for Amperage Draw Failure: Most taillights operate at car
system voltage. Because the taillight system have many light bulbs it will
draw amperage. If the headlight/taillights
have been on for a while they could flicker or go out completely. After the
circuit has cooled the lights might start working again this could mean the main connection
inside the switch is failing when it the contacts get hot. Heat is produced
from amperage being drawn through a switch and resistance has risen due to
the age of the switch. If this condition is occurring the switch should be replaced. Even
when the contacts are cleaned the same problem will return in a
short amount of time.
Preferred Procedure: Replace front and rear taillight bulbs with manufacturers
replacement bulb specification's. If you need to find the correct replacement bulb part
numbers an Auto
Part Store can help.
Common Problems
- Taillight bulbs can be replaced with incorrect bulbs causing dim or no brake light operation.
- If taillights stay on continuously the headlight/taillights switch has
failed and replacement is required.
Check Manufacturer Specific Taillight Questions
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