Dim/dull headlight or headlights can be dangerous as it inhibits the vision of the
driver from seeing obstacles in the roadway. Fortunately there are only a
handful of problems that can cause this issue (most of them simple) which we
will go over in this guide.
What goes wrong?
As headlight systems evolve and become more active to road conditions
brighter and more precise systems demand additional electrical current and computer controls. Corrosion and component wear can cause the headlight beam to be dull
or almost non existent, this is not to be confused with a
headlight lens that is foggy
or if the lens material has degraded.
How much does it cost?
Since headlight systems utilize the vehicles BCM, (body control module), TIPM
(totally integrated power module) IPDM (intelligent power distribution
module) or LCM (lighting control module) depending on the manufacturer. Problems can range from a simple fuse
that is blown, high resistance at an electrical connector, bad ground or
replacement of the aforementioned control module the prices and effort can range
Lets get started!
Problems are listed according to difficulty, Step 1 being the simplest.
When a fuse goes out due to age or a sudden voltage surge when the system
is switched on its best to
check the system
fuse using a test light. This is done with the key in the on position
while the headlight system is energized (on). Locate the headlight system
fuse using the cars owners manual, fuse panel cover or by asking one of
Additionally, there can be
several fuses that control the system, to confirm the fuse or fuses in question a
wiring diagram can be used to identify said fuses such as in the
diagram below. Test and replace any fuse that fails the test (blown or bad
All headlight systems utilize wiring connectors that attach to the
headlight bulb or lens bulkhead connector which is made of plastic, within
this plastic there are metal electrical terminals that reside inside the
connector. Because of the amperage pulled through the circuit these
connections can heat up causing resistance and eventually and bad
connection, this will happen to the power side of the circuit.
To check for
this problem simply remove the connector to inspect for signs of
burnt/melted plastic and discolored (dark) terminals, this is easy to see
and is common. To quickly fix the problem use an Exacto or other sharp
object to clean the electrical contacts on both the headlight bulb and
connector. This will work temporally, the correct repair is to replace both
the headlight bulb and connector.
Headlight systems depend on a proper ground to complete their circuit,
if the ground is dirty or loose it will cause a dim or dull headlight
condition. Many times you can locate this ground by easily following the
wiring harness and observing the "break out" wire that is attached to the
car sub-member or radiator core support. Confirm the connection by removing
the small bolt or screw while cleaning the connection and reinstall, that's
all there is to it.
The headlight switch controls and current flow on older cars while in
newer cars it simply signals a control module. Older cars, remove the
headlight switch to inspect the electrical connector for burned terminals
much like you would the headlight bulb. If burn marks or discoloration is
present replace the switch and the connector. Again cleaning the connection
will help for a short time. Headlight switches on newer cars rarely go out.
Control modules do fail on newer cars causing a dim or dull headlight
operation, to confirm this issue a
(controller area network) needs to be performed.