Headlight Switch
Headlight switches have become more than just a place to turn on your
lights, they
are now used for some diagnostic and programming on your vehicle. In this article
we will tell you what to look for if your headlight switch is failing and some of
the other functions of the switch. Headlight switches used to be a simple pull switch
that turned on the
parking lamps
(running lights) then when pulled all of the way out would turn on the headlights,
or with a twist of the knob would brighten or darken the instrument lamps. On today’s
vehicles the switch has a few more functions thanks to automatic headlights and
the use of on-board monitoring.
One of the first differences you will notice is that the instrument panel
dimmer has been removed from the headlight switch; it is a stand-alone item on most
new vehicles. This is good in that if there is an issue with the instrument lights,
you may not need to replace the entire switch for just a dimming problem. Another
thing you will notice is that there are several different positions to choose from
for the switch depending on the options on your vehicle. There is the usual “off”,
“on” and “running lights”, if equipped with auto-headlights you may see an “auto”
position, when in this position the system uses a light sensor called a “Twilight
Sentinel” (usually in the top center of the dash) to detect if the light levels
require the use of headlights.
Some GM vehicles have a temporary on, this means that when turned to this position
it will spring back to the off position when you let go of it. This is used to enter
the diagnostic/programming mode for the
Tire Pressure Monitor,
consult an
automotive
service manual for the exact procedure. One thing that is still common though
is that a separate switch controls the high-beam lights; on older vehicles it was
on the floor (foot controlled) and newer vehicles use the turn signal lever (multi-function
switch) to turn them off and on.
If you suspect your headlight switch isn’t working properly, the first step as
with any non-functioning electrical item is to get a
test light and check
the
fuses, usually located in the
under-hood
power relay center. If they test ok, you may need to consult a repair manual
to look at the
wiring
diagram. Some new vehicles incorporate headlight fuses, relays and use the BCM
(Body Control Module) to do the actual controlling of the lights, that way they
can take advantage of battery run-down protection and shut the lights off should
you forget to. On older vehicles though, the switch does all of the work, including
the instrument lights.
Auto headlight switches tend to last longer than manual light switches due to
the fact they simply aren’t used as much, they turn themselves on and off. Since
manual switches are only used at night, they will usually last several years. When
replacing your headlight switch always use an OEM (Original Equipment Manufacturer)
or similar high quality part, cheaper switches are made of inferior material and
wont last as long as the high quality replacement. If the switch turns out to be
faulty, most of them can be replaced with a few simple tools, screwdrivers and small
sockets (¼ inch drive) to remove the interior panels to gain access. Many of today’s
vehicles use clips to hold these panels in, so take a good look before starting;
it may save you some headaches.
If further assistance is needed, our certified car repair technicians
are ready to
answer your car questions.
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