Got a brake light out? Anyone
that drives a car should know how to do minor repairs using everyday tools without going to a garage. In this guide we will show you how to replace and
repair your brake bulb system by testing the light socket, fuse, wiring, switch
and BCM. By following this guide you will have the satisfaction of fixing it yourself
and save a considerable amount of money in the process.
When replacing vehicle bulbs use high quality replacement parts to
ensure proper operation and a longer lifespan of the repair. Cheaply made bulbs tend to burn out more
rapidly which requires a repeat replacement.
After testing you may need a replacement bulb or socket and basic tools you
can get from
Amazon or the local parts store when you are ready to
There are basically two styles of bulb replacements which are; The brake lens
needs to be removed to access the bulb, or the bulb socket can be removed by
simply twisting it counterclockwise from the backside of the lens either through
an access hole which is covered by a small plastic panel, or through the trunk, lift back or hatch. We will show you both types and how to test the system in
the following guide.
Before starting park the car on level ground with the emergency brake on.
Checking and Replacing the Bulbs
Have a helper step on the brake pedal to confirm which brake bulb is out;
right, left or high center lights. If none of the lights are working then the
bulb is probably not the problem, though I have seen where all of the bulbs are
out simply because they had gone bad one at a time. When you see a person who has a stop light
out you should do the right thing and tell them, this helps prevent accidents. If
all bulbs are okay and the system is not working then continue with this guide
past the bulb replacement section.
To begin you must determine which style of bulb replacement your vehicle has,
this is done by inspecting the lens and looking for mounting screws which hold
the lens to the vehicle that can be on the side of the lens. You may need to
open the trunk, hatch back, tailgate or lift back.
If no mounting bolts are found on the outside of the lens they will be
located in the back of the rear body panel. You may need to pull back the truck
liner or remove a few plastic trim pieces before these nuts or the bulb socket
is accessible. If no access hole is available you must remove the mounting bolts
and remove the lens to gain access to the bulb. In the case below an access hole was
provided by the manufacturer which makes the job a little easier.
This is what it looks like when the lens is removed.
Now that you have located the light socket and wiring harness its ready to be
removed for testing or repair. On most American made cars and trucks this bulb has two jobs,
both for the brake light and the blinker indicator which will have three wires
feeding the socket; brake, turn signal, and ground wire. On European and
Japanese cars this job is handled separately which will have just two wires,
brake light power and ground.
Grasp the bulb socket and twist firmly counterclockwise, this will allow the
socket to come loose from the lens. Sometimes they can be a little stuck in
which case you can use a pair of pliers to help break it loose.
Once the socket has been removed it will expose the bulb which may have a
burned mark or be a light blue color which indicates a leak in the glass, in either
case the bulb is no good.
Grasp the bad bulb and pull it from the light socket (some bulbs you will
need to push down and twist counterclockwise) then match it to the new unit,
they should by identical. Plug the new bulb in and have a helper push the brake
pedal to see if it works, if it does reinstall it back into the lens and
reassemble the plastic cover or trunk liner and you are all set. If the light is
still not working after replacing the bulb or its dull or dim then more repairs are
needed, continue with the guide.
Testing the Bulb Socket
This is where some testing is needed to repair a bad connection or broken
wire. Start with a test light and secure the ground clip to a known good ground
source such as a bolt or solid metal piece. It's important to get a good connection
free from rust or paint because the test light depends on this conductivity to
work correctly while giving you a good test result. Wiggle the clip so the teeth of the spring
loaded clip dig into the metal to ensure a good connection.
Have a helper hold down on the brake pedal, the remaining working brakes
lights should be on. Use a test light to probe each of the brake light sockets
feed wires; one of them should light up. If you cannot find power then access
the opposite light that is working and probe the wires until power is found to
confirm the test light is working. If power is present at the socket and the
light is still not working continue with the guide. If power cannot be found
skip down to: "Testing the Brake Light System" in this guide.
If you have power at the socket the next step is to check the system ground.
Attach a pointed metal object such as a scribe to the test light clip and probe
the brake light feed wire and the ground wire of the socket, if the tester
lights up the circuit is working and the fault is in the bulb socket
connections. If the test light does not light up there is an open connection in
the ground wire. A bad ground will make the bulb be dim, dull or not work at
all; if the connections are loose the bulb will flicker. A loose connection can be fixed
by enhancing the spring tension on the socket terminals.
You can either make a new ground wire connection by cutting the wire and
making a new ground wire to any metal part near the socket, or follow the wiring harness
and look for obvious damage or cuts in the wiring and repair as needed.
Next, remove the bulb socket and inspect the electrical connector for burned
or melted terminals, this is caused by high resistance creating an open
connection causing the bulb not to work. If damaged or melted, the connector with pigtail
wires will need to be replaced which you can get from
Amazon or from the dealer for
about $35.00 bucks. With the foot off of the brake pedal cut the harness and
splice in the new connector.
Next, inspect the bulb socket; many times this socket will be subject to heat
and corrosion. Manufacturers will install dielectric grease into the socket to
help protect the connection, but with time this clear or brown grease will melt out
and expose the connectors to the atmosphere causing rust or corrosion creating an open connection. Use a
sharp object such as an Exacto knife to scrape the connection clean. This with
help the bulb terminals connect to the socket allowing the bulb to work again, if this socket is badly damaged it should be replaced.
With all connections cleaned or socket replaced and the power and ground checked
with any repairs made to the wiring or connections reassemble the socket and bulb
onto the wiring harness. Have a helper step on the brake pedal to confirm the
bulb operation. Then reinstall the bulb socket back into the lens and reinstall the lens if needed
and you are all set.
Watch this video that gives you an idea of what you are in for when replacing
a bulb before
you begin. Then follow down the guide to learn what to
look for when none of the lights are working.
Testing the Brake Light System
If no power can be found in the brake light system then the problem is
further down in the electrical circuit. Most American cars are designed with the lower brake light circuit wiring incorporated
into the turn signal switch where the brake light bulb and the turn signal bulb
are one and the same. The turn signal switch interrupts the brake light circuit
and installs the blinker circuit when the switch is activated. Japanese and European
auto makers design separate brake and turn signal electrical systems.
Reasons for lack of system power
Blown brake light fuse
Broken wire in the harness
Body control module BCM failure
Turn signal or multi function switch failure
Brake light switch failure
Begin by using a test light to
check the brake light system fuse in the fuse panel which can be identify by the
owners manual or on the lid of the panel. Replace the fuse if it's blown, this
could be caused by a shorted wire to ground, a melted socket or a weak fuse. If
the fuse is okay
continue down the guide.
This is an example of melted terminals on the bulb.
Next in the process is the brake light switch which completes the circuit
when the pedal is depressed by the driver. Locate the switch near the upper part
of the pedal; it will have wiring connected to it. This switch simply connects
the circuit once the pedal is depressed connecting power to the lighting system
which are on vehicles using a BCM or lighting module which uses a ground trigger
that is monitored by the body or lighting control module which in turn powers
the brake lights.
Begin by inspecting the wiring harness, look for obvious
damage such as a cut, wear mark or broken wire indicating the harness has rubbed against a metal frame
causing the failure. Wiggle the wiring while pressing the brake pedal down to
see if you can get the lights working, this would indicate an internal broken
wire. If everything looks okay use a test light or voltmeter and get a wiring diagram from an online repair manual
such as Mitchell1
or search Google Images.
Using the diagram to test for power or ground (depending on the vehicle)
entering the switch on the connector side, then reinstall the connector to the
switch and test through it. If no connection is made the switch is bad and needs
replacement, this is a common failure.
On American vehicles the brake light circuit is routed through the turn
signal switch which can go bad not allowing the currant flow to continue to the
brake lights. Using the wiring diagram test the color wires that are ingoing and
outgoing to see if the circuit is working, if not replace the switch, this is
sometimes called a multifunction switch.
signal switch replacement
On vehicles using a lighting or BCM module use a
wiring diagram to test the ingoing signal from the switch and the outgoing
voltage output to the lights. If no outgoing signal is found and the remainder
of the lights is working the module is bad and replacement is required. If none
of the lights are working check the fuse for the BCM or lighting module.
If a brake light flickers it's because the power
or ground is being obstructed momentarily. The most common cause for this is a loose
fitting bulb socket, while a helper holds down on the brake pedal,
move the bulb around slightly in the socket, if the bulb flickers replace or repair
the socket as needed, also wiggle the wiring.
A brake light system in most cases is a basic electrical system involving a
simple positive and ground connection controlled by a switch which rests in the open position
and then closes (electrical contacts connected) when the pedal is depressed.
A brake lens and socket can melt and distort when the brake lights are kept on
for an extended amount of time, avoid allowing the brake light to stay on overnight.
Check out our
bulb repair forum where our online mechanics have answered thousands of your questions.